Methyltestosterone is a man-made form of testosterone, a naturally occurring sex hormone that is produced in a man's testicles. Small amounts of testosterone are also produced in a woman's ovaries and adrenal system.

Methyltestosterone is used in men and boys to treat conditions caused by a lack of this hormone, such as delayed puberty or other hormonal imbalances. Methyltestosterone is also used in women to treat breast cancer that has spread to other parts of the body.

Methyltestosterone may also be used for purposes not listed in this medication guide.

Do not use this medicine if you are pregnant.

You should not use methyltestosterone if you have prostate cancer or male breast cancer.

Follow all directions on your prescription label. Your doctor may occasionally change your dose to make sure you get the best results. Do not take this medicine in larger or smaller amounts or for longer than recommended.

While using methyltestosterone, you may need frequent blood tests.

Methyltestosterone can affect bone growth in boys who are treated for delayed puberty. Bone development may need to be checked with x-rays every 6 months during treatment.

Store at room temperature away from moisture and heat.

You should not use methyltestosterone if you are allergic to it, or if you have:

• prostate cancer;

• male breast cancer; or

• if you are pregnant or may become pregnant.

To make sure methyltestosterone is safe for you, tell your doctor if you have:

• an enlarged prostate;

• breast cancer;

• heart disease, congestive heart failure;

• liver or kidney disease; or

• if you take a blood thinner (warfarin, Coumadin, Jantoven).

FDA pregnancy category X. methyltestosterone can harm an unborn baby or cause birth defects. Do not use methyltestosterone if you are pregnant. Tell your doctor right away if you become pregnant during treatment. Use effective birth control while you are using methyltestosterone.

It is not known whether methyltestosterone passes into breast milk or if it could harm a nursing baby. You should not breast-feed while using this medicine.

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Follow your doctor's instructions about any restrictions on food, beverages, or activity.

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Methyltestosterone may cause serious side effects. Call your doctor at once if you have:

• changes in skin color;

• increased or ongoing erection of the penis;

• shortness of breath (even with mild exertion);

• swelling, rapid weight gain; or

• liver problems--nausea, upper stomach pain, itching, tired feeling, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).

Women using methyltestosterone may develop male characteristics, which could be irreversible if treatment is continued. Stop using methyltestosterone and call your doctor at once if you notice any of these signs of excess testosterone:

• acne;

• changes in menstrual periods;

• male-pattern hair growth (such as on the chin or chest);

• hoarse or deepened voice; or

• enlarged clitoris.

Common side effects (in men or women) may include:

• breast swelling;

• headache, anxiety, depressed mood;

• numbness or tingly feeling; or

• increased or decreased interest in sex.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Other drugs may interact with methyltestosterone, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell each of your health care providers about all medicines you use now and any medicine you start or stop using.