What to Know About Proscar (Finasteride)

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Proscar (finasteride) is a medication used to treat an enlarged prostate due to benign prostatic hyperplasia (BPH). First approved by the U.S. Food & Drug Administration (FDA) in 1992, Proscar is a 5a-reductase inhibitor that blocks the enzyme that converts testosterone into dihydrotestosterone.

A potent androgen (male hormone), dihydrotestosterone can promote prostate growth, causing BPH. Finasteride is used to shrink the prostate gland, which helps to reduce symptoms such as increased urination, a weak or interrupted urine stream, painful urination and ejaculation, urinary retention, and incontinence.


Proscar is approved to treat BPH in men who are experiencing uncomfortable symptoms due to an enlarged prostate. It helps to reduce the risk of acute urinary retention and minimizes the need for surgery. Proscar is sometimes prescribed alongside the alpha-blocker Cardura (doxazosin) to reduce the risk of symptomatic progression of BPH. 

The medication does not cure BPH, but it does shrink the prostate gland and reduce symptoms over time. It can take up to six months for symptoms to improve.

Off-Label Uses

Finasteride, the pharmacological agent in Proscar, is available in lower doses as the drug Propecia, which is used to treat male pattern baldness.

Finasteride has also been investigated for treating hirsutism (excessive body hair) in women, which is common in those with polycystic ovary syndrome (PCOS). However, more research is needed to confirm it is safe and effective.

Finasteride is sometimes used in transgender hormone therapy along with estrogen for male-to-female transitions; however, it is not approved for this use.

Research suggests finasteride may play a role in the prevention of prostate cancer, but is not approved for this use.

Before Taking

If your healthcare provider suggests you take Proscar, tell them if you have or have ever had prostate cancer or liver disease. Do not take Proscar if you are allergic to finasteride or any ingredients in Proscar. 

Tell your healthcare provider and pharmacist about any other medications, vitamins, or nutritional supplements you are taking.

Precautions and Contraindications

Proscar should not be used by women. Women who are pregnant or may become pregnant should not touch broken or crushed tablets, since this drug may cause harm to unborn baby boys. If you're pregnant and accidentally get finasteride powder on you, wash it off thoroughly and call your healthcare provider.

Proscar is metabolized primarily in the liver, and people with abnormal liver function should use caution when taking the drug.

Your healthcare provider will monitor serum prostate-specific antigen (PSA) levels while you are taking Proscar. While the drug can cut PSA levels in half, research suggests this reduction may mask prostate cancer. Any increases in PSA levels that occur after taking Proscar should be evaluated further, even if they fall within the normal range.

Proscar should not be taken in conjunction with Avodart (dutasteride), another 5a-reductase inhibitor that is used to treat enlarged prostate and hair loss, and as hormone therapy for transgender women. Proscar inhibits type II 5a-reductase, while Avodart inhibits both types I and II 5a-reductase.


When taken for enlarged prostate, the standard dose of Proscar is 5 milligrams (mg) once a day. It can be taken with food or on an empty stomach. If you miss a dose, skip the missed dose and take your next dose at the appropriate time. Do not make up a missed dose by taking a double dose.

Proscar comes in a 5 mg film-coated tablet. As a generic, finasteride comes in 1 mg and 5 mg tablets. 

Side Effects

Since Proscar alters testosterone levels, sexual side effects can occur and may be troubling for men. In fact, one study found that one-third of patients stop using the drug due to sexual side effects such as:

  • Decreased sex drive
  • Trouble getting or keeping an erection
  • Ejaculation disorder

Testicle pain, skin rashes, and depression have also been reported as side effects of Proscar.

Finasteride may also affect breast tissue in men (and women who accidentally come in contact with it), including producing an increase in breast size and breast tenderness. See your healthcare provider if you experience lumps or pain in your breast or nipple discharge.


Allergic reactions may occur and have serious or life-threatening effects, including anaphylaxis. Call 911 if you have trouble breathing or swallowing, or if you experience swelling of your lips, tongue, throat, or face. If you develop a rash, itching, or hives, call your healthcare provider immediately.


Proscar and all 5a-reductase inhibitors contain a warning of an increased risk of being diagnosed with high-grade prostate cancer. A 2003 study in the New England Journal of Medicine found finasteride, the generic equivalent of Proscar, reduced overall prostate cancer risk, but also significantly increased the odds of being diagnosed with a more aggressive form of the disease. Since then, numerous follow-up studies have shown differing results.

In the Prostate Cancer Prevention Trial, 18,000 men ages 55 and older were given either 5 mg finasteride daily or a placebo. After seven years, those taking the medication had a 25% reduced likelihood of developing prostate cancer. 

However, the data also showed a 68% higher risk of being diagnosed with a higher grade of prostate cancer. The study authors concluded that while finasteride may prevent the disease, it may lead to an increased risk of higher-grade cancer. 

Further research—part of a 2019 long-term follow-up analysis of the trial—found the men in the finasteride group had a 25% lower risk of death by prostate cancer than those who took a placebo.

What's more, a different 2018 follow-up study found Proscar’s benefits lasted long after men stopped taking the drug. Researchers used Medicare claims to follow the original study participants and found that, after an average of 16 years, men in the finasteride group had at 21% reduced risk of prostate cancer diagnosis, even after they stopped taking the medication. 

While the latest research suggests the benefits outweigh the risks, the FDA has not approved Proscar for the prevention of prostate cancer. The decision to take a medication for off-label use should be made between you and your healthcare provider, based on your family history of the disease and other factors.

12 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. NIH: National Institute of Diabetes and Digestive and Kidney Diseases. Prostate enlargement (benign prostatic hyperplasia).

  3. U.S. Food & Drug Administration. Highlights of prescribing information: Proscar (finasteride) tablets.

  4. U.S. National Library of Medicine: MedlinePlus. Finasteride.

  5. U.S. Food & Drug Administration. Highlights of prescribing information: Propecia.

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  7. Unger CA. Hormone therapy for transgender patients. Transl Androl Urol. 2016;5(6):877-884. doi:10.21037/tau.2016.09.04

  8. Unger JM, Hershman DL, Till C, et al. Using medicare claims to examine long-term prostate cancer risk of finasteride in the prostate cancer prevention trial. J Natl Cancer Inst. 2018;110(11):1208-1215. doi:10.1093/jnci/djy035

  9. U.S. Food &Drug Administration. FDA Drug Safety Communication: 5-alpha reductase inhibitors (5-ARIs) may increase the risk of a more serious form of prostate cancer.

  10. National Cancer Institute. Prostate cancer prevention – for health professionals (PDQ)

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  12. Goodman PJ, Tangen CM, Darke AK, et al. Long-term effects of finasteride on prostate cancer mortalityN Engl J Med. 2019;380(4):393–394. doi:10.1056/NEJMc1809961

Additional Reading

By Matthew Schmitz, MD
Matthew Schmitz, MD, is a professional radiologist who has worked extensively with prostate cancer patients and their families.