Therapeutic drug monitoring (TDM) receives growing interest in different psychiatric clinical settings (emergency, inpatient, and outpatient services). Despite its usefulness, TDM remains underemployed in mental health. This is partly due to the need for evidence about the relationship between drug serum concentration and efficacy and tolerability, both in the general population and even more in subpopulations with atypical pharmacokinetics. This work aims at reviewing the scientific literature published after 2017, when the most recent guidelines about the use of TDM in mental health were written. We found 164 pertinent records that we included in the review. Some promising studies highlighted the possibility of correlating early drug serum concentration and clinical efficacy and safety, especially for antipsychotics, potentially enabling clinicians to make decisions on early laboratory findings and not proceeding by trial and error. About populations with pharmacokinetic peculiarities, the latest studies confirmed very common alterations in drug blood levels in pregnant women, generally with a progressive decrease over pregnancy and a very relevant dose-adjusted concentration increase in the elderly. For adolescents also, several drugs result in having different dose-related concentration values compared to adults. These findings stress the recommendation to use TDM in these populations to ensure a safe and effective treatment. Moreover, the integration of TDM with pharmacogenetic analyses may allow clinicians to adopt precise treatments, addressing therapy on an individual pharmacometabolic basis. Mini-invasive TDM procedures that may be easily performed at home or in a point-of-care are very promising and may represent a turning point toward an extensive real-world TDM application. Although the highlighted recent evidence, research efforts have to be carried on: further studies, especially prospective and fixed-dose, are needed to replicate present findings and provide clearer knowledge on relationships between dose, serum concentration, and efficacy/safety.

The aims of the study were: 1) the evaluation of the agreement between therapeutic drug monitoring (TDM) and a self-assessment of adherence to psychopharmacological treatments; 2) the identification of predictors of TDM results. Adherence admitted into a psychiatric emergency service (PES) for a relapse of a schizophrenia spectrum disorder (SSD) or a bipolar disorder (BD; DSM-5) was assessed both directly with TDM and indirectly with a self-reported measure (Medication Adherence Report Scale -MARS-10 items). The agreement between TDM and MARS was evaluated. Fifty-seven patients with SSD and 76 people with BD participated in the study. TDM was in range in about 50% of the global sample. No evidence of an association between MARS total scores and TDM results was found. Sensibility, specificity, positive and negative predictive values of almost all MARS total scores were near to 50%. Smoking was strongly associated with a reduction of TDM results within the reference range. In the BD group, female sex was a predictor of TDM in range. In this clinical setting, self-assessment of adherence is neither reliable nor predictive. Furthermore, smoking is a strong predictor of poor adherence to psychopharmacological therapy.