Disclosed herein are non-endogenous, constitutively activated forms of the human 5-HT.sub.2A and human 5-HT.sub.2C receptors and uses of such receptors to screen candidate compounds. Further disclosed herein are candidate compounds identified by the screening method which act at the 5HT.sub.2A receptors. Yet further disclosed is a new class of compounds which act at the 5HT.sub.2A receptors.