[Code of Federal Regulations] [Title 21, Volume 5] [Revised as of April 1, 2007] From the U.S. Government Printing Office via GPO Access [CITE: 21CFR338.10] [Page 234] TITLE 21--FOOD AND DRUGS CHAPTER I--FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) PART 338_NIGHTTIME SLEEP-AID DRUG PRODUCTS FOR OVER-THE-COUNTER HUMAN USE-- Subpart B_Active Ingredients Sec. 338.10 Nighttime sleep-aid active ingredients. The active ingredient of the product consists of any of the following when used within the dosage limits established for each ingredient in Sec. 338.50(d): (a) Diphenhydramine hydrochloride. (b) Diphenhydramine citrate.