Serotonin syndrome

 This potentially fatal condition, caused by having too much serotonin in the central nervous system, is characterized by severe shivering, agitation, mental confusion, copious perspiration, jerking of the limbs, increased reflex actions, dilation of the pupils, rapid heart beat and fever (Ann Pharmacother, 2004; 38: 411–3).

In addition to antidepressants, the worst culprits also include MAO inhibitors, opioids such as morphine and methadone, central-nervous-system stimulants such as amphetamines, 5-HT agonists such as the migraine triptan drugs, and ecstasy and other street drugs.

Some 14–16 per cent of people who overdose on SSRIs develop the syndrome and, at the moment, the best antidote is yet more drugs, including a drug to reduce levels of serotonin.