Mark Colbridge and colleagues discuss overdose of drugs used in depressive disorders and their interactions, including the serotonin syndrome

Depressive disorders are among the most common conditions encountered in medical practice and since the 1950s there has been an increasing number of drugs used in their management. These drugs are thought to act by increasing the concentrations in the central nervous system of certain neurotransmitters, low concentrations of which have been linked with depression. Benefits from the use of antidepressants may not become apparent for two-three weeks after starting therapy. This could be related to gradual changes in the sensitivity of central adrenoceptors, or to concentrations of the drug being built up gradually to an effective level.