The FDA has approved exactly three medications for use as OTC (over the counter) sleep aids: diphenhydramine hydrochloride, doxylamine succinate, and diphenhydramine citrate. All three of these are antihistamines and drowsiness is a side effect.

Diphenhydramine Hydrochloride

FDA approved for use as a sleep aid in 1989. This is the active ingredient in Benadryl, Sominex, and many others.

Doxylamine Succinate

FDA approved for use as a sleep aid in 1978. This is the active ingredient in Unisom Sleep Tabs, Nyquil, and many others.

Diphenhydramine Citrate

This is not sold as a stand-alone sleep aid in the US. It is found in Bayer PM where it is mixed with aspirin, Advil PM where it is mixed with ibuprofen, and Excedrin PM where it is mixed with acetaminophen. BECAUSE OF THE DANGER OF LIVER DAMAGE HAMS RECOMMENDS THAT PEOPLE WHO DRINK ALCOHOL AVOID ACETAMINOPHEN. Advil PM was FDA approved as a sleep aid in 2005.

HAMS Recommendations

25 mg of diphenhydramine HCl and 38 mg of diphenhydramine citrate are to all intents and purposes identical in effect--the only difference is the salt used to bind the diphenhydramine which has no effect after it enters your body. If you feel a need for both a pain killer and an antihistamine to help you sleep then it is far more cost effective to buy a generic version of Benadryl and a generic form of ibuprofen or aspirin than to buy something like Advil PM or Bayer PM where they are premixed for you. AVOID ACETAMINOPHEN BECAUSE OF THE DANGER OF LIVER DAMAGE. Doxylamine is chemically distinct from diphenhydramine and some people may find that one is more effective than the other. We recommend that you avoid name brands which cost much more and buy cheap generics from Amazon or your local stores. If you buy from the HAMS link to Amazon then Amazon will donate a part of the purchase price to HAMS at no extra cost to you.

REFERENCES:

AASM Position Statement: Treating Insomnia with Over-the-Counter Sleep Aids
http://www.aasmnet.org/Articles.aspx?id=253
Accessed November 20, 2009

Rickels K, Morris RJ, Newman H, Rosenfeld H, Schiller H, Weinstock R. (1983).Diphenhydramine in insomniac family practice patients: a double-blind study. J Clin Pharmacol. 23(5-6), 234-42.
http://www.ncbi.nlm.nih.gov/pubmed/6348106

Bayer PM
http://www.wonderdrug.com/products/es/esbpm.htm
Accessed November 20, 2009

Excedrin PM
http://www.excedrin.com/excedrin-pm-drug-facts.shtml
Accessed November 20, 2009

FDA application number 21-393 and 21-394
http://www.accessdata.fda.gov/drugsatfda_docs/nda/2005/021393s000_Advil_PM_MedR.pdf
Accessed November 20, 2009

Insomnia and Its Treatment With Nonprescription Products
http://www.uspharmacist.com/content/tabid/92/s/64/c/12993/dnnprintmode/true/default.aspx?skinsrc=[l]skins/usp2008/pageprint&containersrc=[l]containers/usp2008/simple
Accessed November 20, 2009