Doxylamine

Doxylamine succinate is a highly sedating antihistamine used by itself as a short-term sleep aid, in combination with other drugs as a night-time cold and allergy relief drug, and a preparation is prescribed in combination with Vitamin B6 (pyridoxine) to prevent morning sickness in pregnant women. It is marketed alone as Unisom Sleep Tabs in the United States, and is also one of the active ingredients in NyQuil.

It is a member of the ethanolamine class of antihistamines and has anti-allergy power far superior to virtually every other antihistamine on the market, with the exception of diphenhydramine (Benadryl®). It is also the most powerful over-the-counter sedative available in the United States, and more sedating than many prescription hypnotics. It was found to be superior to even the barbiturate phenobarbital for use as a sedative.

The dosage required to induce hypnosis can be as low as 6.25 mg, but is usually indicated in dosages of 12.5 mg or 25 mg. This drug should never be taken before operating heavy machinery such as an automobile.

Doxylamine succinate is a potent anticholinergic and has a side-effect profile common to such drugs (including drymouth, ataxia, urinary retention, and drowsiness).