Finasteride and PSA levels: what you need to know

Finasteride, sold under the brand names Propecia and Proscar, isn’t just used to re-grow hair. Healthcare professionals also prescribe finasteride for benign prostatic hyperplasia (BPH), a common condition among men where the prostate grows, making it difficult to pee. 

While finasteride can help treat symptoms like difficulty passing urine, it can lower levels of a chemical called PSA in the body. Healthcare providers often test PSA levels to screen for or monitor the presence of prostate cancer, so anything that changes those test results can be a problem. Here’s what you need to know. 

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For people with prostates, healthcare providers typically recommend a PSA screening test every year or two starting in your 50s. This simple blood test, along with a physical exam, can help detect prostate cancer early. 

Finasteride, which is typically prescribed as a treatment for hair loss or an enlarged prostate, works by reducing the conversion of the male hormone testosterone into its more potent form, DHT (dihydrotestosterone). DHT plays an important role in prostate growth. Since PSA is produced by the prostate, blocking it limits prostate growth and reduces PSA levels (Wang, 2020). 

Lowered levels of PSA after treatment with finasteride might present a cloudy picture to a healthcare provider and could mask an underlying disease. In a large study called the Prostate Cancer Prevention Trial, researchers followed over 18,000 participants who had average PSA levels and a healthy prostate. They were assigned to a finasteride or placebo group and had their PSA values checked over the course of seven years. Participants with elevated PSA levels or abnormal rectal exams were sent for a prostate biopsy.

The study found that PSA levels dropped significantly in people taking finasteride for more than one year compared to the placebo group. PSA values dropped by 5% in people without prostate cancer, but up to 15% in those with prostate cancer. Other studies found that finasteride made PSA levels even less accurate in people who already had low PSA to start with (Xu, 2016; Etzioni, 2005).

To make a comparison, let’s say you’ve got a large, troublesome zit. You apply some makeup and cover it up, but the zit is still there lurking underneath. That’s similar to what finasteride does to your PSA levels. It masks the actual amount, falsely lowering test results. That’s important because PSA tests help with the detection of prostate cancer, meaning accurate results are important.

This doesn’t mean you should suddenly stop taking finasteride. But if you’re getting a PSA test, let your healthcare provider know so they can interpret your test results correctly. 

There are different guidelines for PSA levels in people taking finasteride. Some clinical trials found that doubling PSA results made the results more accurate. Your healthcare provider will take your results and your medical history into account when evaluating your PSA levels (Thompson, 2003).

Several studies suggest finasteride may decrease the overall risk of less invasive (low-grade) prostate cancers, but increase the risk of more aggressive or high-grade tumors (Etzioni, 2005; Murtola, 2009).

A recent review of clinical trials supports this link. However, the available data is limited since most studies are small and it’s unclear exactly what the correlation is (Wang, 2020).  

The U.S. Food and Drug Administration’s (FDA) prescribing information for finasteride currently includes a warning about the increased risk of high-grade prostate cancer. It’s a good idea to speak to a healthcare provider if you’re concerned about this or have a family history of prostate cancer (FDA-a, 2011; FDA-b, 2012).

Finasteride may be used to treat conditions like BPH and hair loss, but its effects on blood tests for prostate cancer detection can be a problem. Let your provider know what medications you’re taking if you’re getting a PSA test so they can accurately interpret your results.

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Current version

February 09, 2022

Written by

Gina Allegretti, MD

Fact checked by

Yael Cooperman, MD

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About the medical reviewer

Yael Cooperman, MD, Ro

Yael Cooperman is a physician and works as a Senior Manager, Medical Content & Education at Ro.