Yes, and by studying how these drugs act upon the brain we are beginning to understand better what causes nightmares and how to prevent them. One way to understand nightmares is to consider the conditions that induce them. Children with cerebral palsy frequently complain about nightmares. War veterans, with or without brain injury, frequently report combat-related nightmares as a major component of what is now called post-traumatic stress disorder (PTSD).  Marijuana has been shown to reliably reduce insomnia and nightmares in patients suffering from PTSD. Prazosin is also an effective option for combat-related PTSD nightmares. The beneficial actions of these two drugs, marijuana and prazosin, provides some insight into the mechanisms that underlie the appearance of nightmares. Prazosin blocks a specific type of norepinephrine receptor. It is most often used to improve urinary flow in elderly men with enlarged prostates. VA hospitals have found that that prazosin treatment alleviates two common symptoms of elderly male war veterans, i.e. impaired urinary flow associated with an enlarged prostate and nightmares. The role of norepinephrine in nightmares is also supported by the discovery that yohimbine, a drug that increases the activity of norepinephrine neurons in the brain, increases the number of PTSD-related nightmares. 

Obviously, nightmares occur while we’re sleeping. Scientists have divided sleep into two general phases: rapid eye movement (REM) and non-rapid eye movement (non-REM) sleep. These two phases alternate throughout the night with non-REM sleep predominating during the first few hours after falling asleep. Most, but certainly not all, dreaming occurs during REM sleep. Any medication that reduces the amount of time the brain spends in REM sleep can induce the brain to respond with REM rebound. For example, alcohol reduces REM sleep. Thus, if you fall asleep drunk, the alcohol in your blood prevents your brain from dreaming until the alcohol is metabolized and no longer influences brain function. Once this happens, the brain spends a larger percentage of time in REM sleep, i.e. REM rebound.  Dreams that occur during REM rebound tend to be nightmares. The withdrawal from drugs that share alcohol’s actions at the receptor for the neurotransmitter GABA, such as most of the benzodiazepines, including the popular drugs Klonopin, Ativan or Restoril, also induces nightmares even though they do not always produce REM suppression. Ironically, drugs that are prescribed to treat alcohol addiction by blocking GABA receptors, e.g. baclofen (sold as Gablofen or Lioresal) produce vivid nightmares. Taken together, this evidence suggests an important role for GABA, and the medications that influence it, in the control of nightmares.

The duration of each REM sleep period that a person experiences each night is tightly controlled by the actions of the neurotransmitter acetylcholine. Drugs that antagonize the action of acetylcholine, directly or indirectly, tend to produce nightmares. Unfortunately, lots of medications inadvertently antagonize acetylcholine, including anti-histamines, some of the tricyclic anti-depressants and cardiovascular medications commonly prescribed to reduce blood pressure, the popular anti-ulcer drug ranitidine (Zantac), some common anti-psychotic medications, such as olanzapine (Zyprexa), as well as drugs to prevent motion sickness. The newer anti-depressant paroxetine, Paxil, has the highest incidence of nightmare production; it acts by preventing the reuptake of serotonin, thus implicating a role for this neurotransmitter system as well. Because so many people take one of these common medications daily, the probability to experience recurring drug-induced nightmares is quite high.

Why do some nightmares involve the terrifying feeling of being buried alive or the feeling that it is difficult to breath because there's a monster sitting on your chest (Fuseli's painting)? These suffocating dreams of suffocation usually occur during non-REM sleep when your respiration and heart rate are significantly slowed down. If you are dreaming while experiencing these physiological conditions, your brain incorporates their sensory qualities into your dream narrative. Sometimes, just being tightly wrapped up in your bed sheets provides a sufficient sensory stimulus, due to reduced respiration, to induce the dream experience of suffocation.

In summary, drugs that enhance the function of norepinephrine or serotonin (and probably dopamine) neurons, drugs that impair the function of acetylcholine neurons, highly unpleasant memories, alcohol and most of the drugs we use to reduce anxiety of induce drowsiness, or even overly type bed sheets can all induce nightmares. Given how widespread the use of many of these drugs has become it is amazing that most of us do not experience a nightmare every night.

© Gary L. Wenk, Ph.D.  is the author of The Brain: What Everyone Needs to Know (2017) and Your Brain on Food, 2nd Edition, 2015 (Oxford University Press).

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