What is Finasteride (Propecia) Used For? Side Effects and Dosage


What is Finasteride (Propecia/Proscar)?

Finasteride, also marketed under the trade names Propecia and Proscar, is an antiandrogen medication used in the treatment of benign prostatic hyperplasia (BPH), male pattern hair loss, and transgender hormone therapy. As an antiandrogen, it falls in a class of medications referred to as 5-alpha-reductase inhibitors, or 5-ARIs; these work by blocking the transformation of various steroids in the human body. Finasteride was introduced to the market in 1992, and is manufactured and marketed by the U.S. pharmaceutical company Merck & Co.

What is It Used For?

Finasteride, as mentioned above, is a 5-ARI antiandrogen, meaning its mechanism of action has been established as blocking the activity of Type 2 and Type 3 isozymes of the human enzyme 5-alpha-reductase. This group of isozymes are responsible for the transformation of various hormones in the body, especially the androgen testosterone, the precursor to the potent steroid dihydrotestosterone (DHT), which is used in the growing of tissues in areas such as the prostate gland and hair follicles. By inhibiting the activity of these compounds, Propecia has been used successfully in the treatment of prostate enlargement (BPH), male pattern hair loss (male baldness), hirsutism (excessive hair growth in women), and transgender hormone therapy for transgender women. As early antiretroviral medications used in the treatment of HIV, such as indinavir, zidovudine, and efavirenz, caused hair loss as a potential side effect, finasteride has been prescribed as a treatment in such cases; however, interactions between finasteride and some antiretroviral medications have been shown in some cases to produce a minor reduction in its efficacy.

How to Take Propecia

Finasteride (Propecia) is available in the form of small 1 or 5 mg tablets, taken orally by swallowing. The tablets should not be crushed or chewed, and ingestion should be avoided after the expiry date on the packaging. The drug is intended to be taken by men only, unless otherwise prescribed by a health care professional. It should be taken with a glass of water but is readily absorbed by the body and may be taken with or without food. Typically, finasteride takes up to three months to fully have the desired effect, and efficacy is maximized with sustained, frequent doses. This medication has not been shown to be affected by grapefruit juice.

Finasteride Side Effects

Like other medications, finasteride has been associated with side effects. While side effects have been observed rarely in its use as a treatment for BPH, other uses of finasteride have been associated with some severe side effects and increased risks of certain conditions. Prospective patients should advise their health care provider regarding any other medications they may be taking, as these can interact with Propecia and increase the likelihood of adverse effects.

The following side effects have been observed more frequently:

  • decreased libido
  • erectile dysfunction
  • dizziness
  • asthenia (weakness)
  • headache
  • rash
  • swelling in hands or feet

The following side effects occur less frequently, but may require immediate medical attention:

  • depression
  • breast cancer symptoms, such as breast swelling, discharge, or lumps
  • thoughts of suicide or self-harm
  • allergic reaction symptoms such as hives, shortness of breath, or face swelling

In addition to the above, Finasteride has been shown to increase the risk of prostate cancer in men, due to its ability to stop the behaviour of certain enzymes in the prostate gland, which can mask certain signs of prostate cancer growth. Pregnant women are advised to avoid any exposure to finasteride, including ingesting tablets or even being in the presence of broken tablets, as the antiandrogen behaviour of the drug can cause severe hormone issues in developing male fetuses.


Finasteride, as used in the treatment of male baldness, is intended for use in men aged 18 to 41. The dosage in such treatment is typically one 1 mg tablet, taken once per day. In the treatment of BPH, the dosage is one 5 mg tablet, taken once per day. The duration of treatment is to be determined in each case by the respective health care provider. To reduce the risk of finasteride overdose, missed doses should be skipped and the regular dosing schedule should be resumed the following day. Patients should never take a double dose.

Disclaimer: Please note that the contents of this article are for informational purposes only and should not be considered medical advice. This article, and other AIDS and HIV Information articles on AIDS Drugs Online, are not written by AIDS Drugs Online or reviewed by its staff for medical validity. All views and opinions expressed by the third-party authors are not endorsed by AIDS Drugs Online or its staff. Always consult a medical professional for medical advice.


Reset your password

Please enter your email below, and we will send you a new password.

Still having trouble signing in?

If you're unable to reset your password, please call Customer Service at 1-888-243-7675.