Q. I know that melatonin is a hormone secreted by the pineal gland in larger amounts during the night. Should I try it for sleep?

A. The National Center for Complementary and Alternative Medicine requested a report on this topic from the Agency for Healthcare Research and Quality. Dr. Nina Buscemi and associates at the University of Alberta reported.

Part one of the report covered primary sleep disorders — those not due to other medical or psychiatric conditions — and was published in the Journal of General Internal Medicine in December 2005. The staff did worldwide electronic searches and hand searches for all melatonin studies ever done, and even looked for unpublished studies. This is important because studies that show negative results are much less likely to be published in journals, so analyzing only published studies would artificially magnify the benefits of drugs or vitamins.

Buscemi and her team mathematically combined the results of the most accurate studies — randomized trials — into the only meta-analysis to date of melatonin for primary sleep disorders, and found that it did not help folks sleep. It seemed to work only for the so-called delayed sleep phase syndrome. This is where you fall asleep too late, though your sleep itself is good. You could sleep well late into the morning, while the usual insomniac still has restless sleep in late morning. But only 1 in 10 insomniacs have delayed sleep phase, and the evidence for melatonin in this syndrome is weak, being based on only two studies of fewer than 30 people.

Part two of the report — on sleep disorders due to illness or drug abuse, or lack of sleep due to lifestyle or work schedules, shift work, or air travel — was published in the British Medical Journal in February 2006.

Melatonin was found to be ineffective for all the above. It did not help those with jet lag or shift work fall asleep sooner or get better quality sleep, but part two did not measure daytime fatigue. Two other systematic reviews of jet lag that measured both daytime fatigue and sleeplessness found that melatonin did improve symptoms.

Natural melatonin from animal pineal glands may be contaminated with a virus and should be avoided. Though melatonin appears safe when used for a few weeks, adverse reactions of supplements are underreported compared with drugs. Users may equate ''natural'' with "safe'' and not attribute an adverse reaction to supplements.

The safety of melatonin when used for months or years is unknown. It may contain harmful additives or impurities. In the European Union, melatonin is considered a medicine and is available only by prescription. Avoid it in kids and in adults with seizures or on warfarin.

Dr. Landis Lum is a familypractice physician for Kaiser Permanente and an associate clinical professor at the University of Hawai'i's John A. Burns School of Medicine. Send questions to Prescriptions, Island Life, The Advertiser, P.O. Box 3110, Honolulu, HI 96802; islandlife@honoluluadvertiser.com; or fax 535-8170. This column is not intended to provide medical advice.