Researchers at the National Institute of Mental Health report on an antidepressant with a difference. Ketamine, better known as an anaesthetic, can relieve depression in just hours.

The 'club drug' ketamine may be the fastest-acting antidepressant ever tested, researchers report today.

A team based at the US National Institute of Mental Health (NIMH) in Bethesda, Maryland, studied ketamine in 17 people with major depression. All the subjects had failed to respond to treatment with standard antidepressant drugs or more drastic methods, such as electroshock therapy. But 71% felt better the day after taking ketamine, and 35% still felt better a week later. None improved when dosed with a placebo.

Most striking, the scientists say, was that some patients felt better less than 2 hours after taking ketamine. Currently approved drugs can take weeks to remedy depression. The work is published in the Archives of General Psychiatry.