Overview: antihistamines for sleep

These drugs are commonly used to treat allergies such as hay fever. Like most other first-generation antihistamines, this drug also has a powerful hypnotic effect, and for this reason it is often used as a non-prescription sleep aid; especially in the form of diphenhydramine citrate. This ‘side-effect’ is useful in some people who have difficulty sleeping due to their allergy or who need to treat their allergy and also suffer from poor sleep.

Antihistamines induce drowsiness by working against histamine, a chemical produced by the central nervous system. Most over-the-counter (OTC) sleep aids contain antihistamines. These products are intended to be used for only two to three nights at a time, for example when stress, travel or other disruptions keep us awake. However, tolerance to the sedative effects of antihistamines can develop quickly — so the longer you take them, the less likely they are to make you sleepy.

The main ingredient in OTC sleeping pills is an antihistamine. Common OTC sleep medications include: Diphenhydramine (found in brand names like Nytol, Sominex, Sleepinal, Compoz), Doxylamine (found in brand names such as Unisom, NighttimeSleep aid) and Acetaminophen (found in brand names like Tylenol PM and Aspirin-Free Anacin PM). Others, such as NyQuil, combine antihistamines with alcohol.

Using antihistamine for sleep

Antistamine/OTC sleep aids are meant to be used for short-term insomnia only. Sleep experts generally advise against the use of OTC sleep aids because of side effects, questions about their effectiveness, and lack of information about their safety over the long-term. OTCs can create mental dependency as with any drug over long-term use.

The antihistamines used in OTC sleep aids can produce common side effects, some of them severe. As with any medication, it is advisable to consult your doctor before taking over-the-counter sleep aids. This is especially important if you have glaucoma, trouble urinating due to an enlarged prostate gland, or a breathing problem such as emphysema or chronic bronchitis. Talk to your doctor if you’re currently taking an antidepressant such as a monoamine oxidase inhibitor (MAOI) or did so as recently as two weeks ago. Also check with your doctor first if you take any other drugs for depression or Parkinson’s disease. Women who breast-feed should avoid OTC sleep aids.

Side effects

Side effects might include daytime drowsiness, dry mouth, dizziness and memory problems.

Antihistamines are not as powerful as benzodiazepines or Z-drugs at causing sleep. Also, they may cause a ‘hangover’ effect and some drowsiness in the morning. They may also cause rebound insomnia if you take them for a long time. For these reasons, current UK guidelines do not advise the use of antihistamines to be used solely as a sleeping tablet.

Common side effects of OTC/antihistamine:

  • Drowsiness next morning
  • Dizziness
  • Forgetfulness
  • Clumsiness
  • Feeling out of balance
  • Constipation, urination retention
  • Blurred vision
  • Dry m0uth and thoat


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