A widely introduced pharmacokinetic test in psychopharmacotherapy is therapeutic drug monitoring (TDM). It is especially recommended in patients who are non-compliant, who poorly tolerate, or who do not respond to a medication. It is also useful in patients belonging to the category of "special populations", i.e. somatically ill patients, who are comedicated with a variety of drugs and who suffer from a liver or renal disease, as well as in elderly or very young patients. Increasingly, the use of generics has been shown to represent a source of unexpected treatment outcomes, and TDM may help to explain pharmacokinetic particularities after switching from an original to a generic preparation (or vice versa). Finally, the increasing knowledge of the metabolism of psychotropic drugs allows taking account of the pharmacogenetic status (e.g. cytochrome P-450, P-glycoprotein) of the patients not only in adapting their medication, but also for interpreting pharmacokinetic interactions with clinical consequences. In this respect, pharmacokinetic and pharmacogenetic tests have now also to be considered as a tool in pharmacovigilance.