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Testolactone is a synthetic drug related to the male hormone testosterone . It is used to reduce the size of tumors in some women with advanced breast cancer . Testolactone is available in the U.S. under the brand name Teslac.


Testolactone is used in treating advanced breast cancer in postmenopausal women and in women who have had their ovaries removed. It is never used in treating breast cancer in men.


Testolactone is approved by the United States Food and Drug Administration (FDA), and its cost usually is covered by insurance. It is classified as an antineoplastic agent, which means that it stops or slows the growth of malignant cells. One advantage of testolactone is that, although it is related to testosterone, it does not cause women to develop male characteristics such as a deep voice or facial hair.

As noted above, testolactone is related to the male hormone testosterone. The way in which it inhibits the growth of breast cancer cells is not clear. However, it is known that the hormone estrogen stimulates the growth of some breast cancer cells, and testolactone seems to interfere with estrogen production. The resulting reduction in estrogen levels may slow the growth of breast cancers sensitive to this hormone.

In breast cancer, testolactone is a palliative treatment. This means that it helps relieve symptoms, but does not cure the cancer. It is effective only in about 15% of the women who take it. In these women, however, it helps reduce the size of half or more tumors. Normally testolactone is used along with other chemotherapy drugs for fighting advanced breast cancer.

Recommended dosage

Testolactone comes as a 50 mg tablet. The dose will depend on the patient's body weight and her general health, as well as other drugs she may be taking. However, a standard dose is 250 mg (5 tablets) four times a day for three months. It takes at least several weeks before the drug begins to be effective. Tablets should be stored at room temperature.


People with a history of heart or kidney disease should be sure to tell their doctor, as this may affect their use of testolactone.

Side effects

Testolactone often causes nausea, vomiting, and loss of appetite (anorexia) . Because testolactone must be taken over many months to be effective, people who experience these symptoms should talk to their doctor about medications to relieve the nausea and vomiting so that they can continue to take testolactone.

Other side effects reported with testolactone include numbness or tingling in the toes, fingers, and face, diarrhea , swelling and water retention in the feet and legs, and swelling of the tongue, hair loss (alopecia) , and abnormal nail growth. However, since women who take this drug are receiving other chemotherapy drugs and are in an advanced stage of cancer, it is difficult to pinpoint whether testolactone is exclusively responsible for some of these side effects.


Many drugs interact with nonprescription (over-the-counter) drugs and herbal remedies. Patients should always tell their health care providers about these remedies, as well as any prescription drugs they are taking. Patients should also mention if they are on a special diet such as low salt or high protein. They should not take calcium supplements, since testosterone already has the potential to increase circulating calcium to dangerous levels.

Testolactone may increase the effect of anticoagulants (blood thinning medication). In women where cancer has spread to the bones, testolactone may increase the circulating level of calcium in the body. Calcium levels need to be tested regularly.

Tish Davidson, A.M.



Cancerous. Malignant cells tend to reproduce without normal controls on growth and form tumors or invade other tissues.


A pair of female reproductive organs that release eggs. They are the main source of the female hormone estrogen.


Older women who no longer menstruate because of their age.


The main male hormone. It is produced in the testes and is responsible for the development of primary and secondary male sexual traits.