Two medications used to treat benign prostatic hyperplasia (BPH) belong to a class of drugs known as 5-alpha-reductase inhibitors, or 5-ARIs. The drugs, finasteride (Proscar) and dutasteride (Avodart) can lower prostate-specific antigen (PSA) levels by about 50 percent. If not taken into account, this can interfere with the results of PSA tests to detect prostate cancer.
Men should have a PSA test prior to starting treatment with any 5-ARI so that subsequent PSA values can be interpreted in light of this baseline value. If a man is taking a 5-ARI and no baseline PSA level was obtained, his current PSA test results should be doubled to estimate the “true” PSA level.
A PSA level that falls less than 50 percent after a year of treatment with a 5-ARI suggests that the drug is not being taken as directed or that prostate cancer might be present. Similarly, an increase in PSA levels while taking a 5-ARI suggests the possibility of prostate cancer. PSA values return to their true level after the 5-ARI is stopped.
The medication Propecia, which is a lower dose of finasteride marketed for the treatment of male pattern baldness, also lowers a man’s PSA value to the same extent as Proscar. Men who use Propecia should alert their physician so their PSA results can be adjusted accordingly.