Written by Eva Hamrud, PhD
October 3, 2019
19 min read
Topic Review: Cannabis
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TOPIC INTRO
Pot. Grass. Mary Jane. Dope. Reefer. Ganja. Chronic. Those are just a few of the hundreds of slang nicknames we as a culture have come up with to describe cannabis, the drug derived from the flowering plant of the same name.
Thousands of years have passed since humans started consuming cannabis as a drug, but for much of the past century it’s been deemed illegal to sell in most countries. In the U.S., for instance, it’s still considered a Schedule 1 drug, placing it in the same category as heroin and ecstasy. It’s only been in the last decade that public opinion has shifted toward support of legalization, and over the last few years a couple states and countries have legalized cannabis for non-medicinal consumption. To give you an idea of how much public opinion has changed, consider the fact that nearly every Democratic presidential candidate now supports federal legalization. Just a few short years ago there were virtually no mainstream politicians who adopted that position.
As the fight for legalization rages on, there’s constant public debate about the dangers and benefits of consuming cannabis. Its proponents argue that it’s safe and tout its medicinal properties. Its opponents claim it’s a dangerous, addictive drug that ruins lives.
We at Metafact turned to our pool of medical experts to help us sort through the scientific literature on the subject. So before you roll up some hash and “torch up,” take a few moments to review the best evidence science has to offer on what harm, if any, cannabis will inflict upon you.
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NUMBERS
Meta-Index
188,000,000 Number of people who use marijuana worldwide in 2017
3.8% Proportion of the global adult population that has used cannabis in the last year
14% Proportion of US adult population using cannabis in the last year
10,000,000 Daily users of marijuana in the United States
10.1% Proportion of 8th grade high-school students that have used marijuana
37.1% Proportion of 12th grade students that have used marijuana
11 US states that have legalized recreational marijuana
33 US states that have legalized use of medical marijuana
62% Proportion of US voters who think marijuana should be legalised
$10,800,000,000 Total sales of legal cannabis in the US in 2018
$10,100,000,000 Total sales of ice cream in the US in 2018
$66,300,000,000 Estimated legal cannabis market worldwide by 2025
ORIGIN STORY
Ancient Chinese Healing Herb
For its supposed healing characteristics, cannabis has been used for thousands of years. The first case recorded was by Chinese Emperor Shen Nung in 2800 BC. From the Indian Hindus to the Greeks, ancient texts have claimed therapeutic benefits for health conditions, including arthritis, depression, amenorrhoea, inflammation, pain, absence of appetite and asthma.
Cannabis is a generic word used to indicate the Cannabis sativa plant’s several psychoactive properties. The Mexican word ‘marijuana’ is often used to refer to cannabis leaves or other crude plant material.
It wasn’t until 1841 that cannabis was brought to the West via Irish doctor William Brooke O’Shaughnessy. In the 1920s, western countries started to ban the use of cannabis. The film Reefer Madness was released in the US, demonising cannabis as a highly addictive drug that caused mental disorder and violence. A year later, US Congress passed the Marijuana Tax Act of 1937 – effectively banning it’s production, distribution and use.
In the 1940s, scientists discovered that cannabis contains of a set of at least 66 compounds now known as cannabinoids. The main psychoactive cannabinoid in the cannabis plant is trans-DELTA9-tetrahydrocannabinol or “THC”. THC is the compound that get’s you ‘high’. Cannabidiol (CBD) is another major constituent of the cannabis plant, but doesn’t impact your mental state like THC. Medical marijuana typically refers to CBD extract as it is non-intoxicating. CBD oil is a concentrate of cannabinoids obtained by solvent extraction of the plant or resin.
Medical use of CBD continued with some promising early results around epilespy. By 1996 California legalised medical marijuana, sparking a trend towards legalization across the western world.
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META TRENDS
Legal US Marijuana sales
META TRENDS
“Should the use of marijuana be legal?” US responses
META TRENDS
Proportion of US women using marijuana in the last year
THE CONSENSUS
Is recreational marijuana use safe?
Read the full answers to this question here. There are all sorts of reasons people give for consuming cannabis-based products, but a sizable portion of its users smoke or eat it just for the fun of it. So the first question we posed to our experts was whether recreational marijuana use is actually safe.
Our experts were pretty torn on the question, with several quibbling over the term “safe.” Safe compared to what? “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.),” wrote Matthew Springer, a professor of medicine at the University of California, San Francisco.
But that’s not to say that marijuana causes no harm. For one, millions of users consume it via smoke inhalation. “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, including fine particles that cause cardiovascular morbidity and mortality,” Springer noted.
As with all drugs, the health risks posed by cannabis are somewhat dependent on the frequency of use. Libby Stuyt, an expert from the University of Colorado Denver, wrote that heavy marijuana users are more likely to suffer from suicidal thoughts and “appear to have significant problems with impulse control, concentration, focus, and memory, and say things without really thinking about what they are saying.”
Certain demographics are particularly vulnerable. Several Metafact experts pointed to studies showing that early childhood use can be “associated with lower-than-expected IQ scores and neurocognitive outcomes, including difficulty with attention, impulse control, and executive function.” Research has also shown that those suffering from psychological disorders like schizophrenia are likely to see their symptoms exacerbated by cannabis use.
Several Metafact experts argued that moderate, recreational use of cannabis is mostly safe. “Empirical evidence finds little causal evidence that marijuana increases hard drug use,” noted Luke Chu, an expert from the Victoria University of Wellington. Others questioned the causal relationship between marijuana and bad health outcomes. “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 predisposed to developing these conditions,” wrote Gareth Pryce, an expert from Queen Mary University of London. He cited stats showing that incidents of schizophrenia in the UK have remained relatively stable over a period of decades when cannabis use measurably increased.
And of course there are the potential medicinal benefits offered by cannabis. But we’ll get to those in a few moments.
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THE CONSENSUS
Does marijuana harm the brain?
Read the full answers to this question here. Let’s dive a little bit deeper on the alleged health impacts of cannabis on the human brain. Specifically, does it affect a person’s cognitive abilities, both in the short and long term?
“YES, it can be harmful, especially if used during the vulnerable period of adolescence,” wrote Justine Renard, a neuroscientist from the University of Western Ontario. She pointed to studies showing that use of THC before the age of 17 “can increase the risk of developing important cognitive deficits and psychiatric disorders in adulthood, including anxiety, depression, and schizophrenia.”
Indeed, a few experts pointed to studies showing links between marijuana use and psychotic disorders. “Statistically, there is a robust but moderate association between heavy cannabis use as a youth and the development of psychotic disorders in adulthood,” noted Nehal Vadhan, an expert from Zucker School of Medicine at Hofstra-Northwell. “The likelihood is strongest when: 1) the cannabis a) is very potent, b) starts @ a very young age, and c) is uninterrupted; and the individual had a preexisting risk for a psychotic disorder already.”
Unfortunately, we still don’t know why the two are linked. “Cannabis is not thought to be causal in the development of psychosis by itself – it combines with a number of other risk factors which we still need to understand better,” wrote Nadia Solowij, an expert from the University of Wollongong. “But for some, even single or minimal use of cannabis can trigger a psychosis that may never have developed otherwise, and for young people in particular this is a devastating outcome.”
Some Metafact experts again compared marijuana use to other potentially harmful drugs and deemed it relatively safe. “Yes, THC acts on these important systems but that does not mean the brain is ‘harmed,’” argued Charles Ksir, a professor of psychopharmacology from the University of Wyoming. “Some of the same people who make this argument will prescribe drugs that have profound influences on serotonin, GABA, dopamine, etc and they seem to be less concerned about the long-term consequences of those drug exposures during development, for reasons that elude me.”
It seems clear that pregnant women should steer clear from the drug. Justine Renard pointed to studies showing potential long term cognitive impairment caused from prenatal exposure. “It is important to emphasize that THC is able to cross the placental barrier and to be secreted in breast milk,” she wrote.
But if you’re over the age of 18, the long term impact of cannabis use seems to be limited. Matthijs Bossong, an expert from University Medical Center Utrecht, cited data showing that the negative effects “attenuated with prolonged abstinence, suggesting recovery from the residual cognitive impact of cannabis use.”
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THE CONSENSUS
Is marijuana addictive?
Read the full answers to this question here. There’s been a longstanding debate among the general public over whether marijuana is addictive. It’s likely that at some point you’ve heard the claim from a lay person that it isn’t.
Of course the word “addictive” can mean different things, referring to both physiological and psychological effects. It’s fairly clear that frequent users of THC develop a tolerance from the drug, and they can also suffer from withdrawal symptoms. Ole Rogeberg, an expert from Ragnar Frisch Centre for Economic Research, cited a study in which subjects were given THC capsules every four hours. “They report a rapid tolerance development (within a day or two), and a clear withdrawal syndrome, likened by some of the participants to the flu,” he wrote. “Some reported sleep disturbances for up to 7 days following cessation.”
One expert compared it to alcohol, a substance that doesn’t cause addiction for the vast majority of its users but can induce dependence for some. “There are … millions of people who use cannabis in any of its presentations as a form of relaxation after a day of resolving their conflicts,” wrote Eduardo J. Pedrero Pérez, an expert from Madrid Health. “It can also be combined with other sources of reinforcement (e.g. music, social contact, watching movies), so that it does not isolate the subject, but rather reduces his or her tension. Or it may continue to be limited to certain playful moments, in the company of others, without affecting the rest of the subject’s behavioural repertoire.” Thiago Pianca, an expert from Universidade Federal do Rio Grande do Sul, cited research suggesting that “just about 7-10% of users will become addicted.”
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THE CONSENSUS
Does cannabis use have medicinal benefits?
Read more on this topic from here and here. What about all the health claims around marijuana? After all, plenty of countries and states have passed medical marijuana laws that allow the purchase of the drug with a prescription.
Unfortunately, because of the longstanding laws against marijuana distribution, the studies around its use have been limited in size and scope. Most importantly, government funding of research is low and therefore most of the research is funded by the industry. So many of the Metafact experts relating to cannabis have declared conflict of interests.
There is mixed evidence that cannabis use can have medicinal benefits. Let’s start with anxiety relief – it’s uncertain according to 5 experts so far. CBD to help anxiety is “likely but not yet proven” says Professor Andrea Giuffrida from University of Texas Health and “more controlled clinical studies needed”.
What about relieving pain? There seems more of science to back this up according to 8 experts. “There are numerous studies that show that cannabis reduces pain and improves quality of life of patients with chronic pain,” wrote Alex Bekker, an expert from Rutgers New Jersey Medical School. “For example, a systematic review of randomized controlled clinical trials (766 patients) assessing salutary effects of cannabinoid in treating chronic non-cancerous pain showed significant analgesic effect of these treatment.”
And does Cannabis help with sleep? Sort of. “On the one hand, patients using medical cannabis for different indications, including pain, post-traumatic stress disorder, Parkinson’s disease and other conditions are reporting an improvement in their sleep following cannabis use,” wrote Ran Abuhasira, an expert from Ben-Gurion University of the Negev. “On the other hand, sleep disturbances are among the most frequent complaints of cannabis withdrawal and are a major cause for continued use after attempts to quit.”
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THE CONSENSUS
Is marijuana a ‘gateway drug’?
Read the full answers to this question here. U.S. Surgeon General Jerome Adams recently sparked controversy when he posted a Twitter video in which he made the claim that marijuana acts as a so-called “gateway drug” to harder drugs like cocaine and heroin. This is a claim that’s long been held by marijuana legalization opponents, but is there any science to back it up?
Not really. Luke Chu, an expert from Victoria University of Wellington, noted studies showing that “while marijuana use had increased after the passage of medical marijuana laws, use of other substances like cocaine and heroin did not increase.” In fact, “medical marijuana states experience a relative decrease in opioid addictions and opioid overdose deaths.”
Why does the “gateway drug” myth exist? Mostly because marijuana opponents take a correlation between marijuana and hard drug use and draw a causal relationship where none exists. “A minority of marijuana users will go onto to use other illegal substances but the vast majority will not use the drug more than a few times or will not undertake any further experimentation,” wrote Stuart Taylor, and expert from Liverpool John Moores University.
One possible “gateway” that some Metafact experts suggested was the idea that, because marijuana is illegal in most states, purchasing it involves associating with drug dealers, who may end up pushing the buyer into experimenting with harder drugs. “Legalizing cannabis would actually weaken this one area where the ‘gateway’ effect may operate – this was the rationale behind the Dutch ‘coffeeshop’ system which aimed to separate the markets for ‘soft’ drugs (i.e., cannabis) and ‘harder’ drugs,” wrote Gary Potter, an expert from Lancaster University.
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QUICK ANSWERS WITH CONSENSUS
Is there a net benefit to society from legalising marijuana? – Big debate among the experts here. Some studies suggest legalizing marijuana could increase tax revenue, reduce black market size, and reduce criminalization harms, while other studies highlight potential negative health consequences, increased accidents, and mixed effects on public health and adolescent health.
Is cannabis potency increasing? – Yes Seems so. These studies suggest cannabis potency has consistently increased over time across various regions and forms.
Is long-term cannabis use linked to psychotic disorders? – Yes. These studies suggest that long-term cannabis use, especially frequent and heavy use of high-potency varieties, is linked to an increased risk of psychotic disorders.
Does CBD help Epilepsy? – Yes for a rare form. These studies suggest that CBD helps reduce seizure frequency in various forms of epilepsy, particularly in Lennox-Gastaut syndrome, Dravet syndrome, and treatment-refractory epilepsy, although its exact mechanism remains poorly understood.
Is CBD Oil effective for joint pain relief? – Uncertain. Some studies suggest CBD oil is effective for joint pain relief in animal models and certain cases of osteoarthritis, while other studies show no significant effect compared to placebo in human and canine trials.
Does CBD in food products contain the active ingredient? It depends – buyer beware. These studies suggest that CBD in food products does contain the active ingredient, but the safety, efficacy, and purity of these products are highly questionable.
TOP ANSWER
Does marijuana harm the brain?
Nadia Solowij: A leading expert on cannabis from the University of Wollongong
Likely – if used heavily over a prolonged period of time. While the evidence base for structural changes to the brain is mixed, many studies have consistently found that long-term very heavy cannabis users have smaller volumes of certain regional structures within the brain, with the hippocampus – a region involved in memory function – most consistently affected.
Given the absence of longitudinal studies, that follow people over many years from before they started using cannabis to decades into their cannabis use, we cannot know for certain whether it may be that cannabis users had smaller hippocampal volumes prior to using cannabis and whether this could represent a vulnerability to extensive use. However associations between the extent of cannabis use – number of years used, frequency/quantity of use, and particularly now, dependence on cannabis – and brain structural changes have been found. Similarly for the function of the brain, whether examined by brain imaging methods or traditional cognitive/neuropsychological tests – long term heavy cannabis users are typically impaired in memory function, also attention, decision making, planning etc.
There is evidence that these cognitive and brain functional and structural impairments can improve or revert to normal after a period of abstinence from cannabis, but the evidence is not definitive and there is also evidence of subtle functional alterations to the brain persisting for some time beyond cessation of use. There are also question marks around particular periods of vulnerability to brain harms from exposure to cannabis, for example adolescence when the brain is undergoing many changes toward maturation.
Most of the harms to the brain, even if they are reversible (and there is no reason to suspect that they are permanent), have been found to be associated with exposure to THC – emerging evidence that is really interesting is that CBD may actually protect the brain from the harms associated with THC, and there is significant research ongoing to understand the interaction of these two compounds (and others from the multitude of compounds within cannabis), and their relative proportions or ratios within cannabis.
Of note too, there is substantial evidence from animal research for harms to the brain from exposure to THC, but also exciting growing evidence that CBD may have a range of benefits for brain structure and function in various disease models – not in healthy animals or humans – so we need to be cautious and wary with regard to the proliferation of CBD products used in the general community.
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TAKEAWAYS
- If you’re pregnant or under the age of 17, you shouldn’t consume cannabis on a regular basis.
- Marijuana is less addictive than many other drugs, but that doesn’t mean you won’t develop some sort of dependence on it.
- Be wary of any medical claims made about marijuana so far, since they’ll likely be based on very small studies.
- Using cannabis isn’t a good idea if you suffer from certain psychological afflictions like schizophrenia.
- Occasional, recreational use of marijuana probably isn’t that bad for you, at least compared to other recreational activities like drinking or taking hard drugs.
- Buyers beware of CBD-based products. The active ingredient can vary wildly to those claimed on CBD product labels.
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