This chapter reviews the mechanism of psychotropic medication action, specifically for selective serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants (TCAs), as well as other psychotropic agents. It explores current theories relating to pharmacological action both on the GI tract and centrally. The chapter includes clinical indications, adherence challenges and the interaction with psychological therapies. In such cases, psychotropic medications play a well-attested role in improving global well-being and reducing the symptoms of comorbid psychiatric disorders. TCAs are the most widely used psychotropic agents for pain syndromes. The choice of the right psychotropic agent depends on several factors. The patient's symptom profile is important: for example, given the potentially constipating effect of TCAs, TCAs are recommended for non-constipated patients but serotonin-norepinephrine reuptake inhibitors (SNRIs) for constipated patients. Psychotropic medication can be usefully combined with psychological therapies, but careful thought must be given to how this combination will be managed and explained to the patient.