Sleep Disorders

Sleep Medications: Antihistamines

Antihistimines antagonize central histimine-1receptors. The ones you see in over-the-counter sleep aids are usually diphenhydramine and hydroxyzine. (There are other types of antihistimines that affect H-2, H-3, and H-4 receptors.) People build up tolerance to them over time and when they stop taking them experience rebound insomnia.

During an allergic reaction, action at the histamine receptor sites causes a multitude of body responses. Antihistamines are common drugs that compete for the histamine receptor sites (most commonly H1-receptor sites) in order to block histamine, thus stopping or lessening the allergic reaction. Antihistamines are usually components of OTC allergy and sleeping pills such as Benadryl® or Unisom®, respectively.

Clemastine is indicated for the treatment of allergy symptoms, including rhinitis and pruritus (itching or hives). Although it is a sedative antihistamine, its effects are less intense than many other drugs of this nature. The side effects of clemastine are greatly dependent on the dose, and sometimes can produce contradictory responses. The most commonly reported side effects of clemastine use are dizziness, drowsiness, blurred vision, and dry mouth.

Doxylamine can be used by itself as a sleep aid or combined with other drugs for cold and allergy relief (usually in a night-time formula). It is sometimes used along with Vitamin B6 to avoid morning sickness during pregnancy. Doxylamine is one of the most powerful OTC sedatives in the U.S., more so than some prescription hypnotic drugs. Many patients taking doxylamine encounter dry mouth, nausea, and drowsiness.

Diphenhydramine is widely used in OTC sleeping pills. Many generic sleep aids consist solely of diphenhydramine. It is one of the oldest antihistamines available (classified as a first-generation antihistamine), but surpasses the efficacy of even new prescription drugs. It is sought when a substantial histamine release demands a fast, effective reversal, and is therefore often the drug of choice for allergic rhinitis, motion sickness, insect bites and stings, and hives. Profound drowsiness is a very common side effect, as is dizziness, difficulty concentrating, and urinary retention.

Niaprazine was invented in France, and is used mainly in the European Union. The main use for niaprazine is its intense sedative effect (as opposed to its antihistamine effects). Vertigo and daytime sedation are frequently encountered with the use of this drug.

Pyribenzamine is another first-generation antihistamine, but is being used much less frequently as newer antihistamines arrive on the market. It is indicated for the treatment of hay fever, asthma, urticaria, and rhinitis, and is a mild sedative. Pyribenzamine is known to be abused recreationally with the opiate pentazocine. Common side effects of pyribenzamine use are dry mouth, nausea, gastrointestinal irritation, and dizziness.

Tylenol PM also uses an antihistimine to induce drowsiness. It also incudes acetaminophen, the pain reliever in regular Tylenol.