Doxylamine succinate is a member of the ethanolamine class of antihistamines and has anti-allergy power superior to almost every other antihistamine on the market, with the exception of diphenhydramine (Benadryl). It is also the most effective over-the-counter sedative available in the United States, and is more sedating than some prescription hypnotics. One study found that doxylamine succinate is possibly more effective than the barbiturate phenobarbital for use as a sedative.
This is the active in Nyquill, and unisom tabs (not gel caps). Wallyworld sells the generic for 4 bucks a box, of 32 25mg tabs. Very effective sedative similar to benadryl. Trauma turned me on about a year ago to it. Love the stuff.