Dimenhydrinate. Molecular model of the drug dimenhydrinate. This over-the-counter drug is a combination of the antiemetic (anti-nausea) diphenhydramine (lower left, C17.H21.N.O) and the stimulant chlorotheophylline (upper right, C7.H7.Cl.N4.O2). It is used to prevent nausea and motion sickness, but is also abused for non-medical purposes. Atoms are represented as spheres and are colour-coded: carbon (grey), hydrogen (white), nitrogen (blue), oxygen (red) and chlorine (green).