Non-response, adverse effects and pharmacokinetic interactions with clinical consequences are frequent manifestations observed in psychiatric patients treated with psychotropic drugs. These risks are increased in patients belonging to the category of “special populations”: elderly patients, children and adolescents, patients with a genetic particularity of metabolism or suffering from somatic or psychic comorbidities. Increasingly, the use of generics has been shown to represent a source of unexpected treatment outcomes. Therapeutic drug monitoring (TDM) is not only recommended in these situations, but especially also in patients who are suspected to be non-compliant. In addition, the increasing knowledge of the metabolism of psychotropic drugs allows the use of phenotyping and/or genotyping techniques (e.g. cytochrome P-450, P-glycoprotein) in patients and to adapt their medication considering their pharmacogenetic status. Pharmacokinetic (TDM) and pharmacogenetic tests are therefore useful to solve problems in psychopharmacotherapy and thus improve efficacy and safety of the drugs. An earlier developed Consensus guideline on TDM (Baumann et al., 2004) has recently been updated (Hiemke et al., 2011).