Book excerpt: Clinicians recognize that monitoring psychotropic levels provides invaluable information to optimize therapy and track treatment adherence, but they lack formal training specifically focused on the use of plasma antipsychotic levels for these purposes. As new technologies emerge to rapidly provide these results, the opportunity to integrate this information into clinical care will grow. This practical handbook clarifies confusing concepts in the literature on use of antipsychotic levels, providing clear explanations for the logic underlying clinically relevant concepts such as the therapeutic threshold and the point of futility, and how these apply to individual antipsychotics. It offers accessible information on the expected correlation between dosages and trough levels, and also provides a clear explanation of how to use antipsychotic levels for monitoring oral antipsychotic adherence, and methods to help clinicians differentiate between poor adherence and variations in drug metabolism. An essential resource for psychiatrists, psychiatric nurse practitioners, and mental health professionals worldwide.