Reviewed on 1/12/2022

What Is Finasteride and How Does It Work?

Finasteride is a prescription medication used to treat Benign Prostatic Hyperplasia and Androgenic Alopecia in males.

  • Finasteride is available under the following different brand names: Propecia, Proscar.

What Are Dosages of Finasteride?

Adult dosage


  • 1mg (Propecia)
  • 5mg (Proscar)

Benign Prostatic Hyperplasia

Adult dosage


  • 5 mg orally once daily; assess response after 12 weeks to 6 months

Androgenic Alopecia (Men Only)

Adult dosage


  • 1 mg orally once daily for at least 3 months

Dosage Considerations – Should be Given as Follows: 

  • See "Dosages."

What Are Side Effects Associated with Using Finasteride?

Common side effects of Finasteride include:

Serious side effects of Finasteride include:

Rare side effects of Finasteride include:

  • none 

This is not a complete list of side effects and other serious side effects or health problems may occur as a result of the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may report side effects or health problems to FDA at 1-800-FDA-1088.

What Other Drugs Interact with Finasteride?

If your medical doctor is using this medicine to treat your pain, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider or pharmacist first.

  • Finasteride has severe interactions with no other drugs. 
  • Finasteride has serious interactions with no other drugs. 
  • Finasteride has moderate interactions with at least 15 other drugs. 
  • Finasteride has minor interactions with at least 55 other drugs. 
  • This information does not contain all possible interactions or adverse effects. Visit the RxList Drug Interaction Checker for any drug interactions. Therefore, before using this drug, tell your doctor or pharmacist of all the drugs you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist. Check with your physician if you have health questions or concerns.

What Are Warnings and Precautions for Finasteride?


  • Hypersensitivity
  • Women of childbearing potential

Effects of drug abuse

  • None

Short-Term Effects

  • See “What Are Side Effects Associated with Using Finasteride?”

Long-Term Effects

  • See “What Are Side Effects Associated with Using Finasteride?”


  • Use with caution with obstructive uropathy; carefully monitor patients with large residual urinary volume or severely diminished urinary flow
  • Use caution in liver disease
  • May cause decreased serum PSA in presence of prostate cancer; increases in PSA levels from nadir while on finasteride may signal the presence of prostate cancer and should be carefully evaluated (even if PSA value within normal range)
  • Pregnant and potentially pregnant women should not handle crushed or broken tablets or semen of male partner; may have negative impact in fetal development
  • Rare reports of male breast cancer observed with use; any breast tenderness, enlargement, pain, lumps, nipple discharge or any other type of breast changes should be reported immediately to healthcare provider
  • 5-ARIs and prostate cancer risk
    • June 9, 2011: Recent data from 2 large, randomized, controlled trials observed a reduction in overall incidence of prostate cancer but an increased risk of being diagnosed with a more serious form of prostate cancer (high-grade prostate cancer) in trial participants taking 5-alpha reductase inhibitors (5-ARIs)
    • The 2 trials are the Prostate Cancer Prevention Trial (PCPT) and the Reduction by Dutasteride of Prostate Cancer Events (REDUCE) trial
    • The revised prescribing information recommends that prior to initiating therapy with 5-ARIs, appropriate evaluation should be performed to rule out other urologic conditions, including prostate cancer, that might mimic benign prostatic hyperplasia (BPH)
    • A minimum of 6 months may be necessary to assess response in BPH

Pregnancy and Lactation

  • Therapy is contraindicated in pregnant females and not indicated for use in females; based on animal studies and mechanism of action, drug may cause abnormal development of external genitalia in a male fetus if administered to pregnant female
  • Drug is not indicated for use in females.  
Medscape. Finasteride.

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