Megace (Megestrol acetate) is a man-made substance called progestin which is similar to the female hormone progesterone. It is often used in the treatment of breast cancer. Megace is also used as an appetite stimulant to treat HIV wasting.

Breast cancers are affected by hormones - that is, they rely on supplies of specific sex hormones, such as oestrogen, to grow. On the surface of the cancer cells there are proteins called receptors which are sensitive to the sex hormones. The easiest way to understand the significance of these receptors is to compare the process to that of a lock and key. When the sex hormones come into contact with the receptors they unlock or activate the cancer cells to divide and the tumour grows. Megace disrupts this process in some way. It may be that it prevents the cancer cells from maintaining the receptors on their surface, effectively removing the lock. Or it may have a more direct means of destroying cancer cells that has not, as yet, been identified. The most commonly reported side effect for those patients using Megace is an increase in appetite, causing some people to put on weight. As Megace is an appetite stimulant, (as a side effect) it can sometimes be helpful for people experiencing loss of appetite and weight loss due to advanced cancer.

At the VIIth International Conference on AIDS in Florence, Italy several placebo-controlled studies demonstrated that Megace is effective in producing weight gain in patients with advanced HIV disease.The largest study was a multi-center trial sponsored by Bristol-Myers (the manufacturer). Participating were 278 patients with more than 10% weight loss, anorexia, and absence of infections. Patients were randomized to receive either placebo or one of three doses of Megace (100 mg, 400 mg or 800 mg). Of the first 176 patients analyzed, 62.7% assigned to Megace at 800 mg/day gained more than 5 lbs. Only 16% of patients receiving placebo gained more than 5 lbs. The average weight gain for the group receiving Megace was 7.8 lbs. compared to an average loss of 1.5 lbs. for placebo recipients.

In another study reported in Florence similar weight gains were noted with Megace at doses of 400 mg/day and 800 mg/day, but not at 100 mg/day. Side effects included gastrointestinal upset and impotence in a few patients. Similar results were obtained in a study conducted by the New York Community Research Initiative (CRl), which showed that doses of Megace above 100 mg produced an increase in fat-free mass and body fat, as well as improvement in perceived quality of life. No evidence of a favorable effect on the immune status (T4 cells) or effects which may prevent weight loss during disease complication was noted in this study. Megace is synthetic progesterone. Progesterone is a female hormone. Patients on Megace tend to gain fat, according to studies using therapeutic doses of 800 mg/day. Many people use a lot less than that. A slow weight gain associated with lower than established therapeutic doses may promote gain of muscle mass.