Clenbuterol Hydrochloride and Diphenhydramine Hydrochloride are two completely different drugs.
Cut and paste from Wikipedia:
Converting insoluble amines into hydrochlorides is a common way to make them water- and acid-soluble. This is particularly desirable for substances used in medications. Many pharmaceutical substances are prepared as hydrochlorides so that they may be quickly absorbed in the gastrointestinal tract; the body usually absorbs a hydrochloride within 15 - 30 minutes