Therapeutic Drug Monitoring (TDM) is a valid tool to optimize pharmacotherapy. Individualization of pharmacotherapy is essential in order to optimize efficacy and minimize toxicity, especially for compounds with narrow therapeutic index. The interdisciplinary TDM group of the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP) has therefore worked out consensus guidelines to assist psychiatrists involved in psychotropic drug analysis to optimize the use of TDM of psychotropic drugs. Five research-based levels of recommendation were defined with regard to routine monitoring of plasma concentrations for dose titration of 65 psychoactive drugs: 1-strongly recommended 2-reommended 3-useful 4-probably useful 5-not recommended. Cytochrome P450 phenotyping has been valuable research tool and a way of assessing the genetic basis of metabolic capacity. Phenotyping allows estimation of the total inşuence of drug interaction, genetic polymorphisms, hepatic disease and other factor altering pharmacokinetics. There are characteristic benefits of different methods to assess the pharmacokinetics of psychotropic drugs in clinical practice. TDM measures current plasma concentration and hence summarizes the effect of all pharmacokinetic inşuence, determines the phenotype for the drug currently in use, detects interaction with co-administered drugs. Phenotyping predicts metabolic capacity, provides information about metabolic capacity for a variety of drugs, detects interaction by co-administered drugs. Genotypingas a specific method for mutation, predicts metabolic capacity, provides information about metabolic capacity for a variety of drugs, helps to differentiate noncompliance, and the acquired information has a lifelong validity.