The biggest concern about melatonin concerns its affect on women's fertility, particularly as it's being touted as a substance that will boost fertility. This is because in some animal studies, rats found to miscarry had low melatonin levels (Int J Neuro, February 1992). However, this remains a hypothesis, and taking melatonin may only make things worse. In one animal study of melatonin, mice given melatonin produced pregnancies in which all the embryos in the litter died (J Neur Trans, 1994; 96 (1): 19-29).

Although we can't really draw many parallels in humans from animal studies, some human studies have equally worrying results. Studies have shown that melatonin may reduce levels of follicle stimulating hormone (Mela Res, Nov-Dec, 1991) and raise levels of prolactin (Clin Endo, August 1993).Although it's difficult to know exactly what these alterations mean, Dr David Horriban, director of Scotia Pharmaceuticals, the Surrey based manufacturer of the Efamol evening primrose products, who has performed many studies on altered prolactin levels, says that both effects would have the result of reducing fertility.

Although no one has yet made the connection with melatonin, one study of patients with ovarian cancer found that patients had one thing in common: significantly lower levels of FSH (JAMA, December 27, 1995).

Any questions about the effect of melatonin on female hormones doesn't appear to be preventing the development of a new oral contraceptive (B-Oval) which combines a stiff 75 mg dose of melatonin with progestin. Production will begin as soon as Applied Medical Research (AMR, Fairfax), which owns the concoction, can raise the necessary finance. The endocrinologist who "designed" the contraceptive, AMR's Michael Cohen, takes the view that just because it is free of estrogen, women can now take advantage of a "breast cancer fighting" birth control pill (Science News, May 13, 1995 and Breast Cancer Research & Treatment, March 1995).