Is Recreational Marijuana Use Safe?

Check out this answer from Consensus:

While marijuana has medical potential, its recreational use is not without risks. The evidence suggests that marijuana can have significant cognitive, cardiovascular, perinatal, and quality of life impacts. As the legal landscape continues to evolve, it is crucial to remain aware of these potential adverse effects and to approach recreational marijuana use with caution. Further research is needed to fully understand the long-term safety of marijuana and to provide clearer guidance for both healthcare providers and the general public.

The legalization of marijuana for recreational use has sparked widespread debate about its safety. While some argue that marijuana is a harmless substance, others raise concerns about its potential health risks. This article aims to provide a comprehensive overview of the current scientific understanding of the safety of recreational marijuana use, drawing on recent research findings.

Health Risks Associated with Marijuana Use

Cognitive and Behavioral Effects

Marijuana is often perceived as a harmless drug, especially among young individuals. However, research indicates that marijuana can have significant cognitive and behavioral effects. Cannabinoid receptors are highly concentrated in brain areas involved in cognition and behavior, and exogenous cannabinoids can disrupt these processes, leading to cognitive impairments and behavioral abnormalities2. Observational studies in humans have reported a higher risk of cognitive impairment among marijuana users, raising concerns about its long-term effects on brain health2.

Cardiovascular Risks

Marijuana use has been associated with various adverse cardiovascular events. Studies have shown that marijuana can increase heart rate, blood pressure, and myocardial oxygen demand, potentially triggering myocardial infarctions (MIs) and other acute cardiovascular events6 10. The risk of MI onset is significantly higher in the hour following marijuana consumption, and daily users have an increased annual risk of MI10. Additionally, marijuana use has been linked to other serious cardiovascular events, including sudden cardiac death, cardiomyopathy, and stroke8.

Perinatal and Neonatal Risks

The use of marijuana during pregnancy and lactation poses significant risks to both the mother and the fetus. Marijuana crosses the placenta and passes into breast milk, leading to fetal and neonatal exposure. Studies have found associations between prenatal marijuana use and adverse perinatal outcomes, such as growth restriction, stillbirth, preterm birth, and neonatal intensive care unit admission1 9. Long-term neurobehavioral outcomes in children exposed to marijuana in utero are also a concern, with some studies suggesting potential cognitive and behavioral impairments1.

Quality of Life

The relationship between recreational marijuana use and quality of life (QoL) is complex. While some users may not experience significant changes in QoL, heavy use or cannabis use disorder (CUD) is associated with reduced QoL4. The causal relationship between marijuana use and QoL remains unclear, and further prospective studies are needed to better understand this dynamic4.

Public Perception and Safety Concerns

The increasing legalization of marijuana has led to a growing public perception that it is a safe drug. However, this perception is not entirely supported by scientific evidence. Long-term use of recreational marijuana may be associated with various undesirable side effects, warranting caution from the general public and further research by government and industry sectors5. The potential for adverse health effects, particularly with regular nonprescribed use, highlights the need for a more informed public and healthcare community5.

Is recreational marijuana use safe?

Matthew Springer has answered Unlikely

An expert from University of California, San Francisco in Cardiology

First of all, I feel the answer needs to be more nuanced than simply “likely” or “unlikely” because it’s a complex issue. From the standpoint of marijuana as a recreational drug, based on its recreational use to administer THC to get high, it’s probably safer than many other drugs used for the purpose (heroin, cocaine, methamphetamine, etc.).

However, one point that is frequently overlooked is that marijuana, if smoked, is a source of smoke regardless of the psychoactive properties of THC. It is unsettling how frequently the claim is made that “marijuana has not caused a single death.” This can sound very compelling to those struggling to draw conclusions from what we currently know about marijuana smoke and disease (which is hardly anything). In fact, it would be unusual to see “tobacco” listed as the cause of death for someone who has died of cancer or cardiovascular disease, but we can attribute some of those deaths to tobacco smoke simply because of the vast body of scientific findings that have established this link. If marijuana smoke increases the risk of impaired vascular function, for example, and that contributes to someone’s death via a complex interplay of health conditions, the person will not have officially died of “marijuana.” Much more research is required before a definitive link, or lack thereof, can be concluded.

While the psychoactive substance in marijuana is THC rather than nicotine, marijuana smoke is still the result of dried plant material combustion and contains many of the same thousands of chemicals as tobacco smoke (1), including fine particles that cause cardiovascular morbidity and mortality. Tobacco secondhand smoke (SHS) alone is responsible for ~50,000 deaths in the U.S. each year, with ~46,000 from cardiovascular disease (2-4). Notably, fine particles in marijuana smoke (PM2.5) are similar to those in tobacco smoke and other forms of air pollution; a wide consensus recognizes a link between even several hours of PM2.5 and cardiovascular disease (5).

My research group at UCSF has demonstrated substantial drops in vascular function in rats exposed to even one minute of marijuana smoke at moderate levels to simulate being around other smokers (such as at rock concerts, parties, etc.), regardless of the presence or absence of the cannabinoids, implicating the complex mixture of chemicals in smoke rather than marijuana-specific cannabinoids in the effect (6). While these are rats, not humans, the model is quite good and we have already reported that blood vessels of both rats and humans respond similarly to tobacco smoke (7, 8).

Whether this indicates an actual burden of marijuana smoke exposure on human cardiovascular disease remains to be determined. A variety of scientific studies have searched for ties between marijuana use and cardiovascular effects, with mixed results. For example, a relatively small retrospective study concluded a ~5-fold increase in the risk of a heart attack (myocardial infarction; MI) within an hour of marijuana use (9). A larger cross-sectional study of over 3000 marijuana users revealed a correlation between number of years of marijuana use and the subsequent risk of hypertension or other cardiovascular risk factors (10). On the other hand, the even larger CARDIA study (over 5000 participants (11, 12)) has failed to detect associations between lifetime marijuana use and a subset of cardiovascular disease indications in middle age after controlling for tobacco use. Nevertheless, two preliminary reports about even larger studies from the 2017 American College of Cardiology (ACC) conference reported associations of marijuana use with heart failure (300,000 users out of 21 million people (13)), and with MI (~200,000 users out of 11 million people (14)).

Two recent reviews have concluded that associations exist between marijuana use and cardiovascular indications including cardiac structural and electrical problems, MI, and stroke (15, 16); and a large recent report from the National Academies found limited evidence for increased risk of stroke and MI, with inconclusive evidence for long-term cardiovascular disease risk (17). It’s important to note that correlation studies can make assumptions, such as reliance on cumulative exposure over the years that doesn’t distinguish between infrequent concentrated bursts of heavy use and more constant low-level use, and are limited by the relatively small size of the group currently using marijuana (roughly 20% in the CARDIA study) and the need to rely on statistical methods to isolate effects of marijuana from those of other risk factors. Moreover, the National Academies report came out before the two very large ACC conference reports mentioned above that showed increased risk of heart failure and MI.

Clearly, we still have a lot to learn. However, there is enough evidence from both prospective animal studies and retrospective human studies that marijuana smoke may cause at least some of the harmful cardiovascular effects of tobacco smoke, on both users and bystanders, that it makes sense to avoid exposing yourself, and especially to avoid exposing other people, to your marijuana smoke.

References:

1. Moir, D., Rickert, W.S., Levasseur, G., Larose, Y., Maertens, R., White, P., and Desjardins, S. (2008). A comparison of mainstream and sidestream marijuana and tobacco cigarette smoke produced under two machine smoking conditions. Chem Res Toxicol 21: 494-502.
2. California Environmental Protection Agency (2005). Proposed Identification of Environmental Tobacco Smoke as a Toxic Air Contaminant. Part B: Health Effects. (California Environmental Protection Agency, Office of Environmental Health Hazard Assessment).
3. Barnoya, J. and Glantz, S.A. (2005). Cardiovascular effects of secondhand smoke: nearly as large as smoking. Circulation 111: 2684-98.
4. U.S. Department of Health and Human Services (2006). The Health Consequences of Involuntary Exposure to Tobacco Smoke: A Report of the Surgeon General (U.S. Department of Health and Human Services).
5. Brook, R.D., Rajagopalan, S., Pope, C.A., 3rd, Brook, J.R., Bhatnagar, A., Diez-Roux, A.V., Holguin, F., Hong, Y., Luepker, R.V., Mittleman, M.A., Peters, A., Siscovick, D., Smith, S.C., Jr., Whitsel, L., and Kaufman, J.D. (2010). Particulate matter air pollution and cardiovascular disease: An update to the scientific statement from the American Heart Association. Circulation 121: 2331-78.
6. Wang, X., Derakhshandeh, R., Liu, J., Narayan, S., Nabavizadeh, P., Le, S., Danforth, O.M., Pinnamaneni, K., Rodriguez, H.J., Luu, E., Sievers, R.E., Schick, S.F., Glantz, S.A., and Springer, M.L. (2016). One minute of marijuana secondhand smoke exposure substantially impairs vascular endothelial function. J Am Heart Assoc 5: e003858.
7. Heiss, C., Amabile, N., Lee, A.C., Real, W.M., Schick, S.F., Lao, D., Wong, M.L., Jahn, S., Angeli, F.S., Minasi, P., Springer, M.L., Hammond, S.K., Glantz, S.A., Grossman, W., Balmes, J.R., and Yeghiazarians, Y. (2008). Brief secondhand smoke exposure depresses endothelial progenitor cells activity and endothelial function: sustained vascular injury and blunted nitric oxide production. J Am Coll Cardiol 51: 1760-71.
8. Pinnamaneni, K., Sievers, R.E., Sharma, R., Selchau, A.M., Gutierrez, G., Nordsieck, E.J., Su, R., An, S., Chen, Q., Wang, X., Derakhshandeh, R., Aschbacher, K., Heiss, C., Glantz, S.A., Schick, S.F., and Springer, M.L. (2014). Brief exposure to secondhand smoke reversibly impairs endothelial vasodilatory function. Nicotine Tob Res 16: 584-90.
9. Mittleman, M.A., Lewis, R.A., Maclure, M., Sherwood, J.B., and Muller, J.E. (2001). Triggering myocardial infarction by marijuana. Circulation 103: 2805-9.
10. Yankey, B.A., Rothenberg, R., Strasser, S., Ramsey-White, K., and Okosun, I.S. (2017). Relationship between years of marijuana use and the four main diagnostic criteria for metabolic syndrome among united states adults. J Addict Res Ther: S11:017.
11. Reis, J.P., Auer, R., Bancks, M.P., Goff, D.C., Lewis, C.E., Pletcher, M.J., Rana, J.S., Shikany, J.M., and Sidney, S. (2017). Cumulative Lifetime Marijuana Use and Incident Cardiovascular Disease in Middle Age: The Coronary Artery Risk Development in Young Adults (CARDIA) Study. Am J Public Health 107: 601-606.
12. Rodondi, N., Pletcher, M.J., Liu, K., Hulley, S.B., Sidney, S., and Coronary Artery Risk Development in Young Adults, S. (2006). Marijuana use, diet, body mass index, and cardiovascular risk factors (from the CARDIA study). Am J Cardiol 98: 478-84.
13. Kalla, A., Krishnamoorthy, P., Gopalakrishnan, A., Garg, J., and Figueredo, V. (2017). Cannabis use predicts risks of heart failure and cerebrovascular accidents: Results from the National Inpatient Sample (conference abstract). J Am Coll Cardiol 69: 1784.
14. Chami, A.T. and Kim, C. (2017). Cannabis abuse and risk for myocardial infarction: A population based study (conference abstract). J Am Coll Cardiol 69: 6.
15. Jouanjus, E., Raymond, V., Lapeyre-Mestre, M., and Wolff, V. (2017). What is the Current Knowledge About the Cardiovascular Risk for Users of Cannabis-Based Products? A Systematic Review. Curr Atheroscler Rep 19: 26.
16. Pacher, P., Steffens, S., Hasko, G., Schindler, T.H., and Kunos, G. (2018). Cardiovascular effects of marijuana and synthetic cannabinoids: the good, the bad, and the ugly. Nat Rev Cardiol 15: 151-166.
17. National Academies of Sciences, Engineering, and Medicine (2017). The health effects of cannabis and cannabinoids: The current state of evidence and recommendations for research (Washington, DC).

Is recreational marijuana use safe?

Daniel Malone has answered Unlikely

An expert from Monash University in Education, Pharmacology

How do you define “safe”? What medicines are “safe”? Even water is not safe is you consume enough of it, it could kill you. Yet medicines are used widely and have been responsible for increasing quality of life and life expectancy.

Cannabis is certainly not safe if a person has a predisposition to a psychotic disorder, particularly in adolescence (https://www.ncbi.nlm.nih.gov/pubmed/20590561). Cannabis is not safe for a person that smokes bongs for breakfast every day and becomes severely impacted in terms of mental health as a consequence. Some forms of cannabis are “safer” than others, especially those with higher cannabidiol content, as this may protect against the psychotic effects of other cannabis constituents (https://www.ncbi.nlm.nih.gov/pubmed/27374322).

Cannabis is probably safe in terms of occasional use with higher cannabidiol content in adults with no previous mental health disorders if it is not in a smoked form. Otherwise, cannabis is not “safe”.

Is recreational marijuana use safe?

Libby Stuyt has answered Unlikely

An expert from University of Colorado Denver in Psychiatry

Especially the high potency THC currently available in Colorado. The current marijuana is not like the marijuana of the 60s, 70s, 80s, or even 90s. The flower of most strains available in dispensaries is in the 20-30% THC range with very little CBD. The higher potency leads to increase in addiction rates, especially when people start using in their adolescence.The concentrated products like shatter, dab, oil can be up to 95% THC. Use of these products also lead to greater risk of psychosis.

I have seen severe psychosis from smoking dab in young adults and the antipsychotics are not really effective. Most people require several antipsychotic medications to treat the symptoms. I have also seen a significant increase in suicidal thoughts with those actively using marijuana similar to what is seen in the literature.

It is fairly easy to detect those using the high potency THC on a regular basis. They usually appear to have significant problems with impulse control, concentration, focus and memory, and say things without really thinking about what they are saying. My big concern lately is that bud tenders in dispensaries are basically practicing medicine without a license. A recent study of the dispensaries in Denver found that 69% recommend using marijuana for nausea related to pregnancy. None of this is “relatively safe”.

1.     Freeman TP, Winstock AR. Examining the profile of high-potency cannabis and its association with severity of cannabis dependence. Psychol Med 2015:45:3181-3189.
2.     Regional brain abnormalities associated with long-term heavy cannabis use. Arch Gen Psychiatry 2008;65:694-701.
3.     Dickson B et al. Recommendations from cannabis dispensaries about first-trimester cannabis use. Obstetrics and Gynecology 2018;131:10311038.
4.     Pierre JM Risks of increasingly potent Cannabis: the joint effects of potency and frequency. Current Psychiatry 2017;16:14-20
5.     DiForti et al. Proportion of patients in south London with first-episode psychosis attributable to use of high potency cannabis : a case-control study. Lancet Psychiatry, 2015; doi.org/10.1016/S2215-0366(14)00117-5.
6.     Silins E et al. Young adult sequelae of adolescent cannabis use: an integrative analysis. Lancet Psychiatry 2014;1:286-293.
7.   Kimbrel NA et al. Cannabis use disorder and suicide attempts in Iraq/Afghanistan-era veterans J Psychiatric Research 2017:89;1-5.
8.   https://www.colorado.gov/pacific/sites/default/files/CHED_VS_Health-Watch-No-94-Adolescent-Suicide-in-Colorado-2008-2012_0817.pdf

Is recreational marijuana use safe?

Carsten Hjorthøj has answered Extremely Unlikely

An expert from Mental Health Center Copenhagen in Psychiatry

This is a complicated question, and the answer is no less complicated. However, to try and keep it relatively short: Cannabis, in particular THC, is linked to a range of harmful outcomes: Low level of functioning (e.g. reduced levels of education or work-ability), impaired cognition (possible irreversible if started at a young age), cannabis-induced psychosis, schizophrenia, anxiety, depression, etc. While debate is ongoing as to the extent that these associations represent causal effects, it does seem unlikely that all of them should be explained by factors such as selection or confounding.

Cannabis use is also linked to a range of detrimental outcomes i relation to physical health – and in some cases we do believe that it is beyond the effect of the co-use of tobacco. This includes cardiac problems, possibly cancers, and a cannabinoid-hyperemesis-syndrome with violent vomiting.

Is recreational marijuana use safe?

Kerry Green has answered Unlikely

An expert from University of Maryland in Public Health, Drug Use

Significant research has been accumulating about the adverse short and long-term consequences of recreational marijuana use. Both of these articles are excellent summaries of what we know scientifically about marijuana consequences.

Volkow, N. D., Baler, R. D., Compton, W. M., & Weiss, S. R. (2014). Adverse health effects of marijuana use. New England Journal of Medicine, 370(23), 2219-2227.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4827335/

Hall, W., & Degenhardt, L. (2009). Adverse health effects of non-medical cannabis use. The Lancet, 374(9698), 1383-1391.

http://mobile.legaliser.nu/sites/default/files/files/Adverse%20health%20effects%20of%20non-medical%20cannabis%20use.pdf

In our own work, we have focused on adverse effects for urban, minorities. After matching on background characteristics and behavioral confounders, we have found significant adverse effects over the long-term on social role functioning, sexual risk, drug disorders, and criminal activity.

Stuart, E. A., & Green, K. M. (2008). Using full matching to estimate causal effects in nonexperimental studies: examining the relationship between adolescent marijuana use and adult outcomes. Developmental psychology, 44(2), 395.

Green, K. M., Doherty, E. E., & Ensminger, M. E. (2017). Long-term consequences of adolescent cannabis use: Examining intermediary processes. The American journal of drug and alcohol abuse, 43(5), 567-575.

Green, K. M., & Ensminger, M. E. (2006). Adult social behavioral effects of heavy adolescent marijuana use among African Americans. Developmental Psychology, 42(6), 1168.

Green, K. M., Doherty, E. E., Stuart, E. A., & Ensminger, M. E. (2010). Does heavy adolescent marijuana use lead to criminal involvement in adulthood? Evidence from a multiwave longitudinal study of urban African Americans. Drug & Alcohol Dependence, 112(1), 117-125.

There is also much debate about how effects of marijuana compare to those of alcohol for adolescents. In these two articles, we attempt to answer this question and review what we know to date. To summarize very generally, marijuana use (with alcohol) seems to be worse than alcohol use alone. If marijuana wasn’t harmful, we would expect similar effects since alcohol is held relatively constant.

Green, K. M., Musci, R. J., Johnson, R. M., Matson, P. A., Reboussin, B. A., & Ialongo, N. S. (2016). Outcomes associated with adolescent marijuana and alcohol use among urban young adults: A prospective study. Addictive behaviors, 53, 155-160.

Green, K. M., Musci, R. J., Matson, P. A., Johnson, R. M., Reboussin, B. A., & Ialongo, N. S. (2017). Developmental Patterns of Adolescent Marijuana and Alcohol Use and Their Joint Association with Sexual Risk Behavior and Outcomes in Young Adulthood. Journal of Urban Health, 94(1), 115-124.

Is recreational marijuana use safe?

Bruno Fonseca has answered Unlikely

An expert from University of Porto in Developmental Biology, Cell Biology, Biochemistry

Despite overwhelming public perception of the safety of marijuana use, all drugs may have toxic and/or potentially lethal effects. “The dose makes the poison.” (Paracelsus). As any other substance, the toxicity of marijuana depends on a variety of factors, including how much of the marijuana a person is exposed to, how they are exposed, and for how long. Nevertheless, evidence from animal studies and human case reports appears to indicate that the ratio of lethal dose of marijuana to effective dose is quite large. There has never been a documented human death solely from marijuana overdose. However, various studies have suggested an association of recreational cannabis use with an increased risk of serious cardiovascular events, car crashes, reduced fertility and respiratory problems (if smoked). More controversial is still their association with schizophrenia and psychosis. Overall, marijuana is a relatively safe drug but it has risks.

Is recreational marijuana use safe?

Luke Chu has answered Near Certain

An expert from Victoria University of Wellington in Economics, Econometrics, Health

Empirical evidence finds little causal evidence that marijuana increases hard drug use. For example, Chu(2015) show that while marijuana use had increased after the passage of medical marijuana laws, the cocaine and heroin use did not increase. In fact, heroin use appeared to decrease.

The recent literature on medical marijuana laws (MML) finds that, while these laws have increased marijuana use substantially, they do not cause much negative health and social consequences. For example, marijuana use seems to substitute usage of other substances. Anderson, Hansen, and Rees (2013) find that marijuana use has reduceds alcohol consumption and traffic fatalities involving alcohol. Chu (2015) finds that marijuana is likely a substitute to heroin, as the use of heroin has decreased after the passage of MMLs. Powell, Pacula, and Jacobson (2018) show show that medical marijuana states experience a relative decrease in opioid addictions and opioid overdose deaths. Moreover, Anderson, Rees, and Sabia (2014) find that MMLs reduce suicide rates among younger men, and Sabia, Swigert, and Young (2015) find that MMLs reduce the prevalence of obesity.

Is recreational marijuana use safe?

Robert Carson has answered Unlikely

An expert from Vanderbilt University in Epileptology, Neuroscience, Neurology

The key word here with respect to the Vox article is “relatively” safe.  If by safe, you mean that cannabis use will not directly lead to your death acutely, then it is likely safe, ie. heroin. But excluding that, I don’t believe we can say it is safe.

Data suggests that long-term use of cannabis in childhood may be associated with lower-than-expected IQ scores and neurocognitive outcomes, including difficulty with attention, impulse control, and executive function.  That being said, it is difficult to separate confounding effects of alcohol use as well as socio-economic status in such studies.

Additionally, there are increased reports of “overdoses” with edible cannabis products, likely related to the slow onset of action or to use by children who don’t appreciate what they are eating.  While there may be some debate whether anyone has died directly from this, increased emergency department utilization has been reported, suggesting profound enough symptoms to lead to emergency care.

Empirically, it is hard to imagine that any type of smoke or particulate matter sucked into one’s lungs is good for you.  Indeed, a case-control study from New Zealand does support that “long term cannabis use increases the risk of lung cancer in young adults” AFTER confounding effects of cigarette smoking were accounted for.

Lastly, any substance which impairs judgment brings added risk to activities such as driving, an activity where a brief lapse of concentration or awareness can lead to death or injury.

When used as a medical therapy, the risk/benefit ratio may support use of cannabis (preferably not smoked), but individuals may need to decide for themselves whether the recreational benefits out weigh the potential risks associated with cannabis use.

Is recreational marijuana use safe?

Laurence Mather has answered Likely

An expert from University of Sydney in Pharmacology

The question  “Is recreational marijuana use safe?” is pharmacologically problematical. Being a pharmacologist, I would instinctively respond that no drug can be considered “safe”, but some are “safer” than others, and then I would follow with my own questions “for whom?”, “under what circumstances?” and “compared to what?”.

My first research encounter with cannabis was back in the early 1970s, and this was to analyse its composition with respect to the then-known principal cannabinoids Δ9-tetrahydrocannainol (THC), the principal psychogenic cannabinoid, and cannabidiol (CBD), these days recognised as a non-psychogenic but therapeutically-useful cannabinoid, in material intended for recreational use that had been seized by police. Not surprisingly, the compositions were highly variable! Since then, the science of cannabis has revealed the bodies’ own neurological system with which such molecules interact, those who grow the plants have gained greater expertise, and I have been subsequently concerned only with studying its medicinal properties. My understanding of its “recreational” applications is thus essentially peripheral – so I defer to those who have made this their specialty. I therefore offer the following comments that are developed further in our recent review framed around its medicinal uses https://griffithlawjournal.org/index.php/gjlhd/article/view/756.

Being a plant product, marijuana is comprised of many hundreds of chemical substances, the proportions and amounts of which normally differ depending on the strain of plant, and the conditions of its growth, harvesting, storage, processing, etc. The growing for medicinal use normally standardizes these, so that the end product is reproducible, and leads to a standardised mixture. The growing for medicinal uses also normally precludes the potential for inclusion of harmful chemicals, such as pesticides and herbicides. The chemical composition also depends on the preparation (flowering tops, hot extract, cold extract, etc.) and route (inhaled-transpulmonary smoked, vaporised, oral, sublingual, etc.) used for ingestion. So the effects are the end-product of very many variables, and these should be construed also as a checklist for potential ‘recreational’ marijuana use.

Apart from generally accepted detrimental effects on the developing adolescent brain, and the educational and societal consequences of amotivational effects, it is generally accepted that cannabis/marijuana is (relatively) “safe”, and it is often repeated that “no one has died” as a result of ingesting it. Insofar as laboratory experiments in laboratory animal research provides a guide, THC is of relatively low acute toxicity, with respective median lethal doses (LD50) after intravenous and intragastric administration of 28.8 and 668 mg/Kg in rats, and 42.5, and 482 mg/Kg in mice (Forney RB. Toxicology of marihuana. Pharmacol Rev 23(4):279-284). Scaled to humans, these values indicate an acute toxicity of THC on the scale of grams, compared to normally ingested doses on the scale of milligrams. But this is only for THC. And, besides, although the THC in marijuana is unlikely to stop your breathing, as might result from ingestion of opioids, or stop your heart, as might result from ingestion of amphetamines, it says nothing about its causing such disinhibition or lack of judgement that might stop you walking under a bus or refraining from driving a motor vehicle. And it says nothing about the beneficial or otherwise pharmacology of the other many hundreds of chemical compounds ingested concurrently.

I found the Vox website https://www.vox.com/cards/marijuana-legalization/where-is-marijuana-legal a very sensible resource. Notably, Card 7 is headed Marijuana is a relatively safe drug — with some risks. It then goes on “There are no documented deaths from a marijuana overdose, but that doesn’t mean pot is harmless.” My sentiments, exactly – but clearly, there is still much to learn.

Is recreational marijuana use safe?

Gareth Pryce has answered Likely

An expert from Queen Mary University of London in Neuroscience

The Vox piece is a very balanced summation of currently available knowledge on this subject.

Given the long historical use of cannabis over many years and much research on subject, the likelihood is that moderate recreational use of cannabis for the majority of users is likely to be relatively safe, certainly compared to other legal substances such as alcohol and tobacco. There are caveats, in that cannabis could have effects on the adolescent brain at a time when significant neuronal re-modelling is occurring. Also the development of cannabis strains selected for high THC content (much higher than historical cannabis strains) with low or negligible levels of cannabidiol, which can ameliorate some of the effects of THC may be problematic. The development of these high THC strains is of course a direct consequence of the historical illegality of cannabis.

Much has been made of the link between cannabis use and psychosis/schizophrenia and whilst it is true that cannabis use can trigger these, it is also likely that these individuals are pre-disposed to developing these conditions. This is borne out in the UK, where over the last 50 years, the incidence of schizophrenia in the UK has remained stable and if anything has declined slightly, despite the recreational use of cannabis in the UK being far more widespread over recent years than it was 50 years ago.

Cannabis also has documented medicinal properties for conditions such as multiple sclerosis spasticity (work from my own group), leading to a licensed cannabis-based drug), bladder over-activity and chronic pain and also has neuroprotective properties in experimental studies on a number of neurological conditions. In addition, in a clinical trial of THC as a neuroprotectant in multiple sclerosis, THC showed, in a subset of patients to slow the development of disease progression. The rapid expansion of the properly regulated medicinal cannabis industry bears testament to its therapeutic properties. Cannabidiol is also increasingly being shown to have its own medicinal properties.

No drug is of course completely safe but compared to many others it is certainly safer than the majority and now it is being legalised/decriminalised in an increasing number of countries the evidence is there to be collected as to just how safe it is.

Is recreational marijuana use safe?

Max Hopwood has answered Likely

An expert from UNSW Sydney in Psychology, Social Sciences, Health

The short answer is, it depends!

Cannabis (the drug’s scientific name) has been used around the world for millennia [1]. Historical accounts of cannabis use from China, India, Mesopotamia, Egypt and Celtic Europe testify to the medicinal and spiritual qualities of ‘hemp’. In an ancient Chinese medical treatise from the first century AD, which draws upon material from the period of Shen Nung some three thousand years earlier, an entry advises that “hemp taken in excess makes one see monsters, but if used over a long time, it can establish contact with spirits and lighten the body” [1]. It seems the ancient Chinese believed cannabis has health benefits when the drug is used in moderation.

Moving into the twenty-first century, a review of evidence from 2014 highlights a changing knowledge landscape regarding our understanding of the health effects of cannabis over the past two decades [2]. The author points to the limitations found in research about cannabis and the difficulties with comparing and interpreting study results, particularly regarding causality. To answer the question ‘Is recreational marijuana use safe?’ we need to consider these research limitations, as well as to define what ‘recreational use’ means, and what is meant by the term ‘safe’. However, for the sake of brevity, I will not define these two constructs here; instead, I will interpret the question in its broadest sense.

Research shows that risk associated with cannabis use varies according to many factors including the age at which people start using the drug, the patterns of use that people develop, an individual user’s mental health, how the drug is ingested, and the levels of active ingredients in the drug. Factors such as whether someone uses cannabis with other drugs simultaneously, and whether a user is pregnant, also affect risk.

Studies suggest that it is riskier to initiate cannabis use during adolescence than later, and that daily use is riskier than less frequent use. While cannabis is unlikely to cause psychosis, studies indicate that adolescents with a family history, or personal experience of psychosis, should avoid using cannabis, particularly strains with high levels of THC, the main psychoactive ingredient. While further studies are needed on modes of administration, it is possibly less risky to vaporise or eat cannabis than to smoke it, and there may be more negative health impacts when cannabis is combined with other drugs such as tobacco and/or alcohol. Cannabis use during pregnancy is associated with lower birth weight.

Research reported in the medical journal The Lancet over the past decade [3,4] reveals cannabis use is relatively less harmful when compared to a range of other drugs such as heroin, cocaine, alcohol and barbiturates. In one study, a panel of independent experts assessed harms associated with 20 licit and illicit drugs, on a scale of 0-3.00 and cannabis rated below 1.50 (Nutt et al, 2007). When viewing the distribution of mean harm scores, cannabis comes around the mid-point, indicating that these independent experts viewed cannabis as less harmful than alcohol and tobacco. In a follow up article, which reported a refined analytical method – multicriteria decision analysis – a panel of independent experts again estimated mean harm scores – both personal and social harms – for 20 licit and illicit drugs. On a scale of 0-80, mushrooms were scored as the least harmful drug overall (scored as 6/80) and alcohol was scored as the most harmful (scored as 72/80) (Nutt et al, 2010). The harm score for cannabis was 20/80, where this score comprised almost equal levels of personal and social harms. There are no verifiable accounts of death by cannabis overdose, which stands in stark contrast to many other widely available drugs, including alcohol and opioids.

No psychoactive drug is completely safe for everyone; even for a drug with low harm scores, some people will have adverse reactions when using it, and no one should drive or operate machinery while intoxicated as cannabis affects the brain functions that are required to perform such tasks. The physical, social and dependence-based harms that were measured in the studies above need to be contextualised in relation to an individual’s social and personal circumstances and their patterns of use. For most people, recreational, non-dependent use of cannabis might be relatively safe. The greater risk to individual wellbeing is more likely to come from contact with law enforcement agencies and a criminal conviction for possession and/or use.

References

1. Escohotado, A. (1999). A brief history of drugs. Park Street Press: Rochester, Vermont.
2. Hall, W. (2014). What has research over the past two decades revealed about the adverse health effects of recreational cannabis use? Addiction, 110, 19-35.
3. Nutt, D., King, L. A., Saulsbury, M. A., & Blakemore, C. (2007). Development of a rational scale to assess the harm of drugs of potential misuse, The Lancet, 369 (9566), 1047–1053.
4. Nutt, D. J., King, L. A., & Phillips, L. D. on behalf of the Independent Scientific Committee on Drugs (2010). Drug harms in the UK: a multicriteria decision analysis, The Lancet, 376 (9752), 1558–1565.

Is recreational marijuana use safe?

Maria-Paz Viveros has answered Unlikely

An expert from Complutense University of Madrid in Neurobiology, Addiction, Physiology

One has to be very cautious with this issue, I highly recommend reading this Web page (National Institute of drug abuse)

https://www.drugabuse.gov/publications/research-reports/marijuana/letter-director

See also my answer to the question “Does Marijuana harm the brain?”

Is recreational marijuana use safe?

Ole Rogeberg has answered Likely

An expert from Ragnar Frisch Centre for Economic Research  in Economics

“Safe” is not an absolute, and use of cannabis has its risks. Whether recreational use is “safe” or not thus depends on the level of risk we view as acceptable in a recreational drug. While people will differ in their views on acceptable risks, several groups of researchers have compared cannabis to the legal drugs of alcohol and tobacco along a number of dimensions (dependence, physical and social harms, etc). Based on this, recreational marijuana use appears to carry lower risks all in all than both alcohol and tobacco.

This does not mean that cannabis is harmless, however. Using drugs – whether cannabis, alcohol, tobacco or others – can be viewed as drawing lottery tickets. The user hopes for a reward, but may be unlucky and draw a big penalty as well. The “cannabis lottery” seems to have fewer and smaller penalties than the “alcohol lottery” and “tobacco lottery,” but if you are unlucky that may be small consolation.

An important caveat to this comparison is legal context: Since cannabis remains illegal in most jurisdictions, its use also brings with it legal risks. The comparison above, however, compares the non-judicial risks.

Is recreational marijuana use safe?

Andrew Gunn has answered Likely

An expert from University of Queensland in Medicine

I think the question — “Is recreational marijuana use safe?” — is posed unfairly.

For instance, “Is drinking tea safe?” Obviously not, because millions suffer burns and many children are scarred for life by falling kettles. But it seems churlish to allow small risks to deny the tea drinkers of the world their pleasure.

Similarly, recreational marijuana use has hazards, but there is reasonable evidence that these are significantly less than those of recreational alcohol, a common alternative drug.

I’ve therefore chosen “likely” safe.

Is recreational marijuana use safe?

Michael Roettger has answered Unlikely

An expert from Australian National University in Criminology

As a criminologist, I strongly caution use of recreational marijuana without researching potential criminal liability for 4 reasons:

(1) Recreational marijuana usage is illegal in many jurisdictions around the world, and penalties can range from fines, to long terms in prison, and even possible risk of executation in some countries (e.g., Singapore, Indonesia) when possessing the drug in large quantities. Make sure you check the local law and are aware of the penalties!

(2) Marijuana usage can lead to criminal charges when engaging in activities. It is illegal to drive and operate heavy machinary in many state and federal jurisdictions, and drug driving could be a factor in increasing the severity of criminal charges in cases that might include vehicular homicide. Similarly, it is typically illegal to give illicit drug to minors.

(3) There is not really good way of measuring levels of intoxication when using marijuana by smoking. With alcohol consumption, most packaging provides you with the number of standard drinks consumed, a way to measure intoxication levels. Due to TCH levels varying type of marijuana plant, and smoking leading to unknown levels of intoxication, its possible to consume marijuana above a safe level ( or legal limit if marijuana usage is legal).

(4) Where marijuana is illegal, one must obtain marijuana from a drug dealer and illegal manufacturing methods are often used. This could lead to exposure to toxic substances or contamination of the marijuana being bought. If bought above certain quantities, for example buying for self and friends, this could lead to potentially serious charges of drug trafficking.

Generally, for those who wish to use marijuana recreationally, I suggest using extreme caution and awareness of penalties to minimize harm from the legal consequences of consumption.

Is recreational marijuana use safe?

Sylvan Katz has answered Uncertain

An expert from University of Saskatchewan in Complex Systems Science

Until there is reliable randomized double blind cross-over clinical trials of statistically significant number of participants this question cannot be answered reliably.

Is recreational marijuana use safe?

Julie Moschion has answered Unlikely

An expert from University of Melbourne in Economics

To answer the question “is recreational marijuana use safe?”, one needs to be able to measure the causal impact of marijuana on a variety of outcomes. Essentially, what is the consequence of using marijuana on education, employment, physical health, mental health, housing, children’s development…

Observing that users of marijuana have worse outcomes is insufficient to demonstrate that marijuana is harmful as those worse outcomes may have resulted from other characteristics which may be correlated with marijuana, for example such as having experienced trauma or violence during childhood.

Unfortunately, the literature (at least as far as I know it) is far from being able to answer the relevant causal question at this stage. There is ample evidence that marijuana users have worse outcomes but the causal evidence is still very slim.

When causality is taken seriously, a lot of the correlations observed actually disappear. For example, recent research looking at the relationship between homelessness and marijuana use shows that: (i) only the age of the take-up of marijuana matters (not later transitions in and out of use); (ii) it only matters for boys. Other research shows plausibly causal negative impacts on suicidal ideation, education and life satisfaction.

Overall, marijuana plausibly has negative effects but the magnitude and breadth of those effects are much smaller than thought previously and there is still much to be done to establish clean causality and a number of potential outcomes of interest to be analysed.

Is recreational marijuana use safe?

John Stogner has answered Likely

An expert from University of North Carolina at Charlotte in Criminology, Health

The wording of the question asks if it is “relatively safe.” Though use is not without risk, it is likely relatively more safe than alternative recreational substances (such as synthetic cannabinoids).

Is recreational marijuana use safe?

Michael Lynskey has answered Near Certain

An expert from King’s College London in Addiction, Psychiatry

Recreational or occasional use of cannabis is relatively safe and, in particular, it is safer than recreational use of alcohol.   One of the greatest potential risks associated with the use of this drug centres on its use when driving a vehicle, operating heavy machinery or engaging in other potentially risky behaviours.

For example, a meta-analysis suggested that cannabis intoxication while driving was associated with an approximate doubling in the risk of a motor vehicle accident. This estimate is substantially lower than the corresponding estimates for driving while intoxicated on alcohol, which range from a 6- to 15 fold increase in risk, but are, nonetheless, non-negligible: in general, individuals should avoid driving a motor vehicle while intoxicated on cannabis, alcohol or any other drug.

Long-term, heavy use is associated with the development of a dependence syndrome, which may include experiences of withdrawal if the individual ceases cannabis use. Although less severe than withdrawal from alcohol, the development of dependence means that a small minority of chronic, heavy cannabis users may experience difficulties ceasing cannabis use when they would like to. However, estimates of the proportion of individuals who use cannabis and develop dependence are lower than the proportions of those using tobacco, alcohol or most other drugs who develop dependence.

The vox article points to the alleged ‘gateway’ properties of cannabis and suggestions that the use of cannabis may potentially encourage the use of other drugs: while studies using a variety of strategies have generally been unable to discount this possibility, it is still the case that the majority of those who use cannabis will not progress to the use of other drugs.   Further, Kandel’s initial formulation of this hypothesis also posited that both tobacco and alcohol use encourage cannabis use and subsequent use of other drugs: arguments justifying the prohibition of cannabis based on this association could also be applied to advocate banning tobacco and alcohol.

There is also mounting evidence that cannabis use may be associated with elevated rates of mental health problems including an increased risk for the development of psychosis. While this is of considerable concern, there is evidence that this increased risk may be limited to individuals predisposed to developing psychosis and may be specific to particular types of cannabis: high (THC) potency varieties with low concentrations of CBD. More chronic long term use may also be associated with respiratory illness if the drug is smoked but these risks are less than the corresponding risks associated with tobacco use.

As a previous response has noted, potentially one of the greatest risks of cannabis use derives from its classification in many jurisdictions as ‘illegal’ and individuals caught with even just a small amount of the drug potentially face a range of criminal sanctions.

A response to the question in the end depends on the definition of ‘relatively’ and the extent to which an individual is prepared to expose themselves to some level of risk: as noted above, cannabis use does incur some risks but these risks are substantially lower than risks associated with either alcohol or tobacco use.

Moving forward, a better approach than trying to prohibit all use of cannabis, even infrequent use which appears to be relatively harmless, would be to consider ways to encourage safer patterns of use (e.g., avoid use before driving, consider non-smoked routes of administration and also consider use of strains containing high levels of CBD) while eliminating legal ramifications associated with the use/ possession of this drug.

Is recreational marijuana use safe?

Irene Elkins has answered Unlikely

An expert from University of Minnesota in Addiction

The answer to this is complicated. Recent evidence suggests that marijuana use during adolescence is not safe (e.g., it may precipitate psychotic episodes among vulnerable individuals and affect parts of the brain involved in learning and memory). While occasional use during adulthood may be relatively safer, frequent use has been associated with a number of harmful consequences.

For example, although a recent article of ours primarily addressed the relationship of ADHD to adolescent marijuana and alcohol use (https://doi.org/10.1016/j.drugalcdep.2017.11.011), we reviewed other evidence that “While the trend toward legalizing marijuana helps lower perceptions of its risks among adolescents (Pacek et al., 2015), they may be at higher risk for adverse long-term outcomes from marijuana than adults (Volkow et al., 2014). Those with ADHD appear even less likely to believe that marijuana causes difficulty with thinking and slowed responses (Harty et al., 2015).”

“With increased numbers of marijuana users accounting for the rising incidence of marijuana use disorders (Hasin et al., 2015), developing strategies to reduce frequent use has become increasingly important (Pedersen et al., 2016). Our findings suggest that adolescents with ADHD need better preparation to make informed choices regarding alcohol and marijuana.”

Is recreational marijuana use safe?

Wim Van Den Brink has answered Extremely Unlikely

An expert from University of Amsterdam in Psychiatry, Epidemiology, Addiction

There is no such thing as SAFE use of any addictive substance. There is no safe level of alcohol consumption; WHO only recognized low risk alcohol consumption. There is no safe level of cigaret smoking since even smoking 1 cigaret per dat creats aleady about 50% of the cardiovascular risk of smoking 20 sigarettes per day. recreational cannabis use often goed together with tobacco use (joint) and as such recreational cannabis use is definitly not safe. Vaping or eating have there own problems, but might be less problematic than smoking joints. Finally, it may depent on what kind of cannabis someone is smoking with special risks for some people in the case of high level THC and low levels CBD (skunk).