Melatonin, the wonder supplement being taken for everything from jet lag to insomnia, may interfere with usual sleep patterns.

Scientists from the UK Ministry of Defence warn that indiscriminate use of the supplement, banned in the UK but still freely available in the US, may well cause the sort of sleep problems that it is supposed to treat.

In an experiment with a group of men placed in a closed environment so they did not know when it was night and day the scientists found that those on melatonin started developing an irregular sleep wake cycle.

However, they do accept that the pattern may have been more regular had the men been able to see when it was light and dark (The Lancet, 1996; 348:551).

Doses of melatonin found in health stores in the US are so high that they can cause hypothermia and affect a man's sex drive. Some doses also contain impurities, warned Richard Wurtman from the Massachusetts Institute of Technology, talking at a melatonin workshop.

Researchers explained that nobody understands how melatonin works, and so it was dangerous to take it at will, as many Americans are doing. They said that the supplement should be taken at the lowest possible dosage, and under a doctor's supervision.

The supplement is freely available in the US because of its classification as a dietary supplement.

See WDDTY vol 6, no 11 for more information on melatonin.

!AThe Lancet, 1996; 348: 539.