Dreams may be messages from the subconscious, but many hormones, neurotransmitters and even our blood sugar also affect them. Everyone knows that a heavy meal at bedtime can lead to disturbing dreams, but hypoglycemia (low blood sugar) is also thought to cause nightmares.
Almost all psychiatric drugs can influence our dreaming, but even medications that wouldn't seem suspect such as blood pressure drugs may have an effect - some of them reducing nightmares, some increasing them. Individual differences are, of course, always possible.
How Medications Affect Dreaming
All drugs that affect serotonin levels may affect sleep and dreaming. This goes for most antidepressants, especially the SSRIs like fluoxetine (Prozac) and citalopram (Celexa). Mirtazapine (Remeron) can also cause very peculiar, sometimes disturbing dreams. Dream recall may also be increased. These effects often gradually disappear after a few months of use.
Antipsychotic (neuroleptic) drugs like risperidone (Risperdal) and olanzapine (Xyprexa) can increase vividness of dreams, but often decrease dream recall. Pramipexole (Mirapex), ropinirole (Requip) and other dopamine agonists, used to treat Parkinson's disease, may cause vivid dreams, sometimes of sexual nature.
People taking opioid painkillers like fentanyl or oxycodone often report vivid, realistic dreams, especially when beginning use. Morphine is even named after Morpheus, the Greek god of dreams and sleep.
The hormones DHEA and testosterone may cause nightmares if the dose is too large. Sympathomimetic and stimulant drugs are also associated with nightmares. Even tranquilizers like diazepam (Valium) may paradoxically lead to unpleasant, even aggressive dreams.
Cholinesterase inhibitors like galantamine (Reminyl) and donepezil (Aricept), used in the treatment of Alzheimer's disease, may produce vivid, bizarre dreams and increase recall of dreams. Oxybutynin (Ditropan) and other anticholinergic drugs which are used to treat e.g. urinary frequency have the opposite mode of action and may reduce dreaming and dream recall.
Drugs that Decrease or Increase Nightmares
Many blood pressure drugs influence dreaming, often with opposite effects. Beta blockers such as propranolol (Inderal) and atenolol (Tenormin) may cause nightmares, but alpha blockers/antiadrenergic drugs like clonidine (Catapres) tend to reduce them. The alpha blocker prazosin (Minipress) has been successfully used in studies to reduce nightmares in post-traumatic stress disorder (PTSD).
The anticonvulsant topiramate (Topamax), the antidepressant trazodone (Desyrel), the migraine drugs cyproheptadine (Periacti) and pizotifen (Sandomigran) and MAO inhibitors have also been used to suppress nightmares and other unpleasant dreams. On the other hand, MAOIs, especially the Parkinson's drugs selegiline (Eldepryl) and rasagiline (Azilect), may provoke vivid and disturbing dreams.
Memantine (Namenda), dextromethorphan, riluzole (Rilutek) and other NMDA antagonists may cause surreal or unpleasant dreams, sometimes nightmares. Same goes for the smoking cessation aid varenicline (Chantix). Anticonvulsants (epilepsy drugs) frequently affect the nature of dreams, but the drugs in the class are so different that the effects vary.
Herbs and Supplements That Alter Dreams
Many herbs influence dreaming, especially those with psychotropic effects like kava kava, St. John's wort, valerian, hops and passionflower. The Ayurvedic herb ashwagandha is also well-known for creating surreal dreams. Sometimes herbs like mugwort (Artemisia vulgaris) and African dream root (Silene capensis) are taken specifically for their effects on dreams and dream recall.
Melatonin can produce vivid dreams, but some people have also reported of unusually "normal" dreams that follow everyday logic instead of the surreal patterns of dreams. L-tryptophan and 5-HTP, being precursors to serotonin, may affect dreams similar to serotonergic antidepressants.
Vitamin B6 is well-known for creating detailed, vivid dreams and boosting dream recall. Vitamins B5 and B12 may have similar effects to a lesser degree. Choline and other supplements that increase brain levels of the neurotransmitter acetylcholine can render dreams unusually vivid and make them easier to remember.
Caffeine has been used to induce lucid dreaming, because it makes one sleep lighter. There is, obviously, the possible side effect of taking too much and not being able to sleep at all.
References
Taylor HR, Freeman MK, Cates ME. Prazosin for treatment of nightmares related to posttraumatic stress disorder. Am J Health Syst Pharm. 2008 Apr 15;65(8):716-22.
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