What is the difference between Cetirizine hydrochloride and Cetirizine dihydrochloride?

The active ingredient in both pills is the same (Cetirizine). The difference between hydrochloride and dihydrochloride is the difference between the non active ingredients in the pills that are added to the drug so that there is enough bulk to make a pill. The above 'advice' is simply rubbish. Any (old Skool) A-Level chemistry student knows the difference between 'hydrochloride' and 'di-hydrochloride': Not the same molecule.However, in layman's terms: cetirizine di-hydrochloride is the real thing and is less likely to make you drowsy. Cetirizine hydrochloride is a copycat molecule to work around patent laws.From personal experience, cetirizine hydrochloride makes me drowsy, whereas cetirizine di-hydrochloride does not. :-)