Before taking finasteride, tell your doctor if you have ever had an allergic reaction to this medication, or to a similar medicine called dutasteride (Avodart). Finasteride should never be taken by a woman or a child. Finasteride can be absorbed through the skin, and women or children should not be permitted to handle finasteride tablets. Although finasteride is not for use by women, this medication can cause birth defects if a woman is exposed to it during pregnancy. Finasteride tablets should not be handled by a woman who is pregnant or who may become pregnant. If a woman accidentally comes into contact with this medication from a broken or crushed tablet, wash the area with soap and water right away. Call your doctor at once if you notice any breast lumps, pain, nipple discharge, or other breast changes. These may be signs of male breast cancer.
There may be other drugs that can interact with finasteride. Tell your doctor about all your prescription and over-the-counter medications, vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start a new medication without telling your doctor.

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. Call your doctor at once if you notice any breast lumps, pain, nipple discharge, or other breast changes. These may be signs of male breast cancer. Less serious side effects may include:

• feeling like you might pass out;
•  swelling in your hands or feet; 
• pain in the testicles; 
• impotence, loss of interest in sex, or trouble having an orgasm; 
• abnormal ejaculation; 
• swelling or tenderness in your breasts;
• dizziness, weakness; 
• headache; 
• runny nose; or 
• skin rash. 

This is not a complete list of side effects and others may occur. Tell your doctor about any unusual or bothersome side effect.