NEW YORK (Reuters Health) - Last year's study suggesting hormone replacement therapy could do more harm than good triggered a sharp drop in the number of older women using the drugs, Canadian researchers said Tuesday.

The study in question is the Women's Health Initiative (WHI), a U.S. government-sponsored trial of 16,000 women taking combined hormone replacement therapy (HRT) made up of estrogen and progestin. The trial was stopped in July 2002 after early analysis showed the therapy raised the risk of stroke, heart attack and breast cancer.

While the risk to the individual user was small, researchers estimated the treatment would cause eight additional cases of breast cancer, seven heart attacks, eight strokes, and 18 blood clots in every 10,000 women taking the combined form of HRT for one year, compared with non-users.

In the new study, Dr. Peter C. Austin and his colleagues discovered that in the period immediately following the release of the WHI findings, the number of women older than 65 taking HRT, both old and new users, dropped significantly in Ontario.

This finding "confirmed what we had heard about anecdotally," Austin, who is based at the Institute for Clinical Evaluative Studies in Toronto, told Reuters Health. "Two of the authors are family physicians, and had observed this phenomenon in their practices," Austin added.

Hormone replacement therapy is often used to alleviate the symptoms of menopause, but Austin noted that women older than 65 -- who are many years past menopause -- have also been given HRT to ward off diseases, primarily cardiovascular disease.

Austin and his colleagues obtained their findings by tracking claims for hormone replacement therapy submitted to a universal drug program for seniors in the province of Ontario between 1992 and 2002. This program records the use of medications by all Ontario residents older than 65, totalling 1.3 million people.

The analysis, reported in the Journal of the American Medical Association, looked at the use of combined HRT and the estrogen-only form of the medication, which is prescribed to women who have undergone hysterectomy.

Austin and his team discovered that use of HRT among older women increased until 1999, when it hit a plateau. After the results of the WHI study appeared, however, prescriptions for hormone replacement dropped dramatically, and in the last quarter of 2002, use was 32 percent lower than during the same period a year before.

Austin said he would expect to find the same results among older women in the U.S., given the large amount of publicity the WHI study results received.

SOURCE: Journal of the American Medical Association 2003;289:3241-3242.