Psychotropic drugs, like antipsychotics and antidepressants, are often associated with metabolic side effects such as weight gain and an increased risk of the development of diabetes and an atherogenic lipid profile. These adverse effects not only bear a high cardiovascular risk and lead to higher morbidity and mortality, but are an additional burden to mentally ill patients and can be a decisive factor for the compliance and, consequently, the success of the therapy. Second generation antipsychotics (SGAs), in particular, clozapine and olanzapine, lead to significant weight gain and impair glucose metabolism. Despite the availability of newer SGAs, such as aripiprazole, which are considered to be less prone to cause metabolic side effects, olanzapine is still one of the most prescribed SGAs worldwide. Antidepressant drugs may also induce weight again and diabetes even though the literature is contradictory, probably due to different receptor affinities. This review aims to provide an overview of the metabolic side effects caused by commonly used psychotropic drugs and give insight into underlying mechanisms.