Psychoactive substances are substances that, when taken in or administered into one's system, affect mental processes, e.g. cognition or affect. This term and its equivalent, psychotropic drug, are the most neutral and descriptive term for the whole class of substances, licit and illicit, of interest to drug policy. ‘Psychoactive’ does not necessarily imply dependence-producing, and in common parlance, the term is often left unstated, as in ‘drug use’ or ‘substance abuse’.

The Tenth Revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-10) includes in Chapter V a detailed classification of over 300 mental and behavioural disorders. Its publication follows extensive field-testing by more than 100 clinical and research centres in 40 countries.

There are two main versions available: Clinical Descriptions and Diagnostic Guidelines and Diagnostic Criteria for Research. The former provides clinical descriptions detailing the principal signs and symptoms of each disorder, together with other important but less specific associated features, as well as comprehensive guidelines for their diagnosis. The latter version is intended to help those researching specific disorders to maximize the homogeneity of study groups. To this end, it sets out criteria that allow the selection of individuals with clearly similar symptoms and other characteristics.

• ICD-10 Clinical descriptions & diagnostic guidelines
  This document contains a listing of ICD-10 clinical descriptions and diagnostic guidelines for mental and behavioural disorders due to psychoactive substance use (F10 - F19).
• ICD-10 Diagnostic criteria for research
  This document contains a listing of ICD-10 diagnostic criteria for research for mental and behavioural disorders due to psychoactive substance use (F10 - F19).
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