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What’s the latest on tibolone, the estrogen alternative?

By the Way, Doctor

What’s the latest on tibolone, the estrogen alternative?

(This article was first printed in the April, 2004 issue of the Harvard Women’s Health Watch. For more information or to order, please go to http://health.harvard.edu/women.)

Q What happened to tibolone — the estrogen alternative we heard about a while ago? Did it turn out not to be effective?

A When we first wrote about tibolone in December 2001, many experts anticipated FDA approval within a year or two. That hasn’t happened, and you’re not alone in wondering why.

Few things work as well as estrogen-based therapy for relieving menopausal symptoms, but many women prefer to avoid it because of the health risks. Combined with progestin (as Prempro), estrogen increases a woman’s risk of cardiovascular events and breast cancer. Taken alone, estrogen raises the risk of uterine cancer and, to a lesser extent, breast cancer.

Tibolone is a synthetic steroid whose hormonal effects are said to be “tissue-specific” and thus less risky than estrogen-based therapies. Like estrogen, tibolone protects bone, alleviates hot flashes, and improves vaginal tissues. But it has a protective, progesterone-like effect on the uterus, and it doesn’t increase breast density or tenderness. Tibolone’s cardiovascular effects are murkier. On the positive side, the drug reduces total cholesterol and harmful triglycerides and slightly lowers LDL (bad) cholesterol. But it also lowers HDL (good) cholesterol. Many experts are concerned about this mixed picture.

Organon, tibolone’s maker, has undertaken several large randomized studies to further evaluate the drug’s safety and to assess its effects on fracture risk. In all, more than 10,000 women will participate in these trials.

Since tibolone is used in 70 other countries, why isn’t it available in the United States? The answer lies in the lessons learned from the Women’s Health Initiative’s test of Prempro. Without large randomized clinical trials, assessing a drug’s safety and effectiveness is a calculated shot in the dark. Given what we’ve learned from hormone therapy’s long history, it makes sense that FDA approval awaits further data. It’s also worth noting that the United Kingdom’s Million Women Study found an increased risk of breast cancer in users of all types of hormone-related therapies, including tibolone (The Lancet, Aug. 9, 2003).

— Celeste Robb-Nicholson, M.D.
Editor in Chief, HWHW