In the late 1960s research was begun to develop antidepressant agents that would be selective inhibitors of serotonin reuptake. The antidepressants then available, the tricyclic antidepressants, inhibited the reuptake not only of serotonin but also of other monoamines such as noradrenaline--and it is this activity, together with anticholinergic actions, that is responsible for many of the adverse effects such as cardiac toxicity. After much chemical research a family of antidepressants with similar pharmacological activity but disparate chemical structure was developed by several medicinal research laboratories. Because the selective serotonin reuptake inhibitors are chemically different they do not possess the common structural side-effect profile of the tricyclic antidepressants.