What to Know About Proscar (Finasteride)

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.

Uses

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.

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.

Dosage

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.

Severe

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.

Warnings

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.

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.