INTRODUCTION Current classifications of psychotropic drugs, developed in the 1960s, are based on beliefs about clinical effectiveness. This article evaluates the scientific validity of current drug terms and possible alternative classifications. METHODS A historical, conceptual, and empirical review of the psychopharmacology literature is provided. Consistency of classification is examined by 3 major categories: chemical structure, pharmacodynamic mechanism, and clinical efficacy. RESULTS Current drug terms based on clinical effectiveness are not valid scientifically, either claiming efficacy which is disproven or ignoring other areas of clinical efficacy. Hence, clinical efficacy is not a consistent and scientifically valid way of classifying psychotropic drugs. Chemical structures are also heterogeneous for drugs with similar clinical efficacy. The most consistent way to define drug classes is pharmacodynamic mechanism. Specific drug groups identified are: monoamine agonists ("antidepressants" and "stimulants"), dopamine blockers ("antipsychotics"), second messenger modifiers ("mood stabilizers), and gabaergic agonists ("anxiolytics" or "hypnotics"). CONCLUSIONS Consistent with a recent proposal of psychopharmacology organizations, this article proposes a new nomenclature based mainly on biological pharmacodynamic mechanisms. Specific terms that are scientifically valid and clinically practical are suggested. It is hoped that this new language would allow for more meaningful and accurate communication between clinicians and patients.