Tricyclic antidepressants (amitriptyline, nortriptyline, clomipramine, imipramine and desipramine) and antipsychotics (clozapine). Therapeutic Drug Monitoring (TDM) is based on the assumption that there is a relationship between the blood concentration and clinical effect (therapeutic improvement and adverse effects). It also assumes there is a concentration range of the drug which is characterized by maximal effectiveness and maximal safety, the “therapeutic window”. The Diagnotix kit for measuring tricyclic antidepressants (TCAs) and antipsychotics (PS1) includes the TCAs amitriptyline, nortriptyline, clomipramine, imipramine and desipramine (including the drugs’ metabolites) and the antipsychotic clozapine (including the metabolite norclozapine).The TCAs amitriptyline, nortriptyline, clomipramine, imipramine and desipramine are used for the treatment of several types of depression, obsessive compulsive disorder, neuropathic pain, nocturnal enuresis, and for the prophylactic treatment of chronic tension type headache and migraine. TCAs have a pronounced inter-individual pharmacokinetic variability and a narrow therapeutic window. Studies on the relation between blood concentration and clinical improvement have supported the relation for the TCAs. Systematic reviews and meta-analyses led to convincing evidence of a significant relationship between clinical outcomes and plasma concentrations for the TCAs which are associated with a high probability of response.