Does diphenhydramine make you sleepy
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Does Diphenhydramine Make You Sleepy?
Introduction to Diphenhydramine and Sleepiness
Diphenhydramine, a first-generation antihistamine, is commonly used for its sedative properties. It is often found in over-the-counter sleep aids and allergy medications. This article synthesizes research findings on the sleep-inducing effects of diphenhydramine.
Daytime Sleepiness and Diphenhydramine
Several studies have demonstrated that diphenhydramine can induce significant daytime sleepiness. In a study where healthy subjects were administered diphenhydramine, terfenadine, or a placebo, it was found that diphenhydramine significantly reduced the latency to stage 1 sleep compared to the other treatments, indicating increased sleepiness. Another study confirmed that diphenhydramine produced significant feelings of drowsiness for up to six hours after administration.
Cognitive Impairment and Sedation
Diphenhydramine not only induces sleepiness but also impairs cognitive performance. Research involving a driving simulator and digit symbol substitution tasks showed that diphenhydramine caused significant mental impairment for up to two hours post-administration. This cognitive impairment parallels the sedative effects, suggesting that both are manifestations of the same pharmacologic action.
Acute and Residual Sedative Effects
The sedative effects of diphenhydramine are most pronounced shortly after administration. A study comparing the sedative effects of cetirizine and diphenhydramine found that diphenhydramine caused marked impairment in alertness and performance on the first day of administration, although tolerance to these effects developed by the third day. Additionally, positron emission tomography (PET) scans have shown that diphenhydramine has a significant next-day residual sedative effect, as evidenced by high brain H1 receptor occupancy.
Efficacy as a Sleep Aid
Diphenhydramine is effective in improving sleep parameters such as sleep latency and sleep efficiency. In a study involving insomniac patients, diphenhydramine significantly improved sleep latency and was preferred over placebo despite some side effects. Another study comparing diphenhydramine with a valerian-hops combination found that diphenhydramine significantly increased sleep efficiency and total sleep time during the first 14 days of treatment.
Mechanism of Action
The sedative effects of diphenhydramine are primarily due to its antagonistic action on histamine H1 receptors in the brain. This blockade reduces wakefulness-promoting signals, leading to increased sleepiness and reduced cognitive performance . Studies using H1 receptor knockout mice have confirmed that the sleep-promoting effects of diphenhydramine are dependent on H1 receptor blockade.
Conclusion
In summary, diphenhydramine is a potent sedative that induces significant sleepiness and cognitive impairment. Its effectiveness as a sleep aid is well-documented, although users may develop tolerance to its sedative effects over time. The primary mechanism of action involves the blockade of histamine H1 receptors, which reduces wakefulness and promotes sleep. While effective, the potential for next-day residual effects and cognitive impairment should be considered when using diphenhydramine as a sleep aid.
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