Finasteride (brand name: Proscar) treats benign prostatic hyperplasia, a condition in which the prostate becomes abnormally enlarged. Information from the National Library of Medicine describes finasteride as a member of a group of drugs named for the enzyme they target, 5-alpha reductase. By blocking the activity of this particular enzyme, finasteride prevents it from producing hormones that enlarge the prostate. The drug does not cure the condition, however, and once the medication is stopped, the prostate may begin to enlarge once again. Although the five-milligram dose of finasteride is commonly prescribed for enlarged prostate, the drug is also available in a one-milligram dose to treat hair loss in men.
Rare side effects
The Mayo Clinic notes that rarely patients report having had side effects associated with finasteride. These side effects are not typically serious but if they worsen or continue, contact a physician. Rare side effects include headache, rhinitis (stuffy nose) and back pain. Also, some patients may experience abdominal pain and diarrhea. Patients may feel weak or dizzy. The dizziness results from postural hypotension, a side effect of finasteride that causes blood pressure to drop upon standing. If the condition worsens, fainting or seizures may occur so feelings of dizziness should be monitored closely.
Common side effects
By far the most commonly reported side effect of finasteride deals with sexual function. According to Merck, disruption of sexual function remains the most frequent reason for stopping treatment during clinical studies. Some patients may experience decreased libido and sexual desire. Moreover, men may have difficulty achieving an erection and have less ejaculation, as well as pain in the testicles.
Severe side effects
Severe allergic reactions to finasteride require immediate medical attention. Effects related to drug allergy or hypersensitivity includes pruritis (itching, often related to hives), urticaria (hives), rash and swollen lips and face. Male patients who notice breast changes should consult with a physician. These changes could include an enlargement of the breasts, as well as the presence of lumps or liquid discharge from the nipples. Painful breasts may also indicate an adverse effect of the drug. Merck also notes that finasteride may cause peripheral edema--a swelling of the body's extremities that usually occurs in the legs and feet.