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Meanwhile, other researchers are piecing together an increasingly detailed understanding of melatonin's effects on circadian rhythms, among them, Dr. Al Lewy, a psychiatrist at Oregon Health Sciences University in Portland, who has given melatonin to 120 people. Many sleep disorders, Lewy notes, are caused when normal circadian or daily rhythms go awry. In people with delayed sleep phase disorder, for instance, the problem is falling alseep too late at night and sleeping too long in the morning. In advanced phase disorder, the problem is reversed. Lewy, who, among others, showed that well timed exposure to bright light can remedy such disorders, is trying to use melatonin instead."Giving melatonin is like giving darkness," he says. Taking as little as 500 micrograms before dusk, "tricks the body into thinking it's dark out even if it's sunny," prompting an earlier onset of sleep. Taking it in the morning, "makes the body think dawn has not happened yet."In theory, melatonin, given at the right time of day, might also be used to treat winter depression the mood disorder that affects some people, especially women, when the days are short and the nights long.Although light has been shown to ease winter depression, the link with melatonin is less clear, says Dr. Thomas Wehr, chief of clinical psychobiology at the National Institute of Mental Health, who studies seasonal changes in melatonin levels. As drug companies scramble to bring melatonin based drugs to market, some consumers, impatient with the slow pace of corporate drug development and with scientists who advise not taking the melatonin products now available as nutritionalsupplements while standing to profit if melatonin becomes a drug, are taking matters into their own hands.Some manufacturers are profiting already. The Life Extension Foundation in Hollywood, Fla., now fills 500 mail orders a day for melatonin, says vice president Bill Faloon, who takes it himself.Other desperate insomniacs and weary travellers get their supplies from Cardiovascular Research, Ltd. in Concord, Calif. and Nutrition Headquarters Inc. in Carbondale, Ill. Should they?Of course not, the experts say at least on the record.To be sure, it is widely agreed that "one of the nice things about melatonin, from a purely toxicological point of view, is that it is extraordinarly safe," says Dr. Steven Paul, vice president for drug discovery at Eli Lilly.But even at low doses, melatonin can trigger release of prolactin, a hormone that can cause menstrual irregularities . More research is needed to determine the right doses for sleep and jet lag taking the wrong dose, or even the right dose at the wrong time, could make jet lag worse.Worse still is the spectre of a repeat of the L tryptophan disaster of 1989. This other natural soporofic, widely sold in health food stores, was eventually found to have caused the deaths of 38 people and serious connective tissue disease in 1,500 more. Granted, the problem was not Ltryptophan itself but impurities that crept in during manufacturing by one Japanese firm. But bad manufacturing could happen with melatonin too, or any other supplement not produced according to manufacturing processes approved by the US Food and Drug Administration. "People are opening themselves up to potential disaster if they take it now," adds Oren of NIMH. "The terrible thing with tryptophan could replay itself." But some researchers, while issuing stern caveats in public, admit privately they take the stuff themselves.And the National Nutritional Foods Association, the trade group for 4,500 of the nation's health food suppliers and retailers, which a year ago took the unusual step of suggesting health stores not sell melatonin, has now had a change of heart.Some stores pulled melatonin from their shelves after that warning, but last week the group's science director, Burton Kallman, said his concerns "have been dissipated to some extent.. . If people want ta sell it over the counter, it does not look to me like a harmful product." So what should you do? The prudent thing, says nutritionist David Schardt of the Washington based Center for Science in the Public Interest, is to wait for more studies. But unless your melatonin product is impure, the worst you're likely to experience is sleepiness the next day if you take too much, or or worsened jet lag if you take it at the wrong time. "As far as we know," he says, "there is no evidence anyone could die from this."