Mebhydrolin or mebhydroline is an antihistamine

Antihistamine

An H1 antagonist is a histamine antagonist of the H1 receptor that serves to reduce or eliminate effects mediated by histamine, an endogenous chemical mediator released during allergic reactions...

. It is not available in the United States, but it is in various other countries. It is also called Bexidal (BD) and Diazolin (RU). It is used for symptomatic relief of allergic symptoms caused by histamine release, including nasal allergies and allergic dermatosis.

Mebhydrolin has been shown to enhance the performance-deficit effects of alcohol.