Although one is used for male pattern baldness and the other for disease of the prostate, both Propecia and Proscar contain finasteride. Finasteride works by blocking a key step in the activation of testosterone. By blocking this conversion, there is a drop in the blood levels of an activated form (dihydrotestosterone) without an effect on blood levels of testosterone. So all of the functions of testosterone (such as libido, fertility, and muscle strength) are not usually affected. Dihydrotestosterone (DHT) is involved in the growth of cells in the prostate, leading to enlargement also known as benign prostatic hyperplasia. DHT is also responsible for male pattern baldness.
Propecia is usually given at a dose of 1 milligram of finasteride a day for male pattern baldness. Proscar is usually given at a dose of 5 milligrams a day for prostate enlargement. Both Propecia and Proscar can lower the levels of PSA (also known as prostate specific antigen). PSA is a marker in the blood for prostate cell growth. It is frequently increased in men with prostate cancer. Normal blood levels of PSA depend on the age of the man. Most laboratories usually consider a level of less than 4 to be normal. Propecia may falsely reduce the levels of PSA by 0.5-0.7. Proscar can reduce the blood level of PSA by up to 50 percent.
It is important for men taking either Propecia or Proscar to let their physicians know they are on these drugs. The drugs affect the interpretation of the blood levels of PSA.
