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Finasteride: 7 things you should know

Medically reviewed by Carmen Fookes, BPharm. Last updated on May 24, 2022.

1. How it works

  • Finasteride, depending on the brand, may be used to treat benign prostatic hyperplasia (BPH) or hair loss in men.
  • Finasteride works by blocking an enzyme called Type II 5α-reductase which is responsible for converting the hormone testosterone into dihydrotestosterone (DHT). This results in increased levels of testosterone and decreased levels of dihydrotestosterone. An overabundance of dihydrotestosterone has been implicated in benign prostatic hyperplasia (BPH) and prostate cancer.
  • The scalp of men with androgenetic alopecia (male pattern baldness) has also been found to contain increased amounts of DHT and miniaturized hair follicles compared with men who have a lot of hair. Finasteride reduces scalp concentrations of DHT and appears to interrupt a key factor in the development of androgenetic alopecia in those men who are genetically predisposed.
  • Finasteride belongs to the class of medicines known as 5-alpha reductase inhibitors.

2. Upsides

  • Finasteride 5mg tablets (brand name Proscar) are indicated for the treatment of symptomatic BPH in men with an enlarged prostate. Finasteride reduces lower urinary tract symptoms such as daytime urinary urgency, frequent nighttime voiding, urinary hesitancy, weak stream, straining, and prolonged voiding). Finasteride lowers the risk of needing to have prostate surgery. May be used in combination with doxazosin in men with symptomatic progression of BPH.
  • Finasteride 1mg tablets (brand name Propecia) are used for the treatment of male pattern baldness - also called androgenetic alopecia. Finasteride is indicated for hair loss in MEN only.
  • Significant increases in hair count at both 6 and 12 months have been reported in men treated with finasteride 1mg tablets (an average increase of 107 hairs when compared to placebo [a pretend pill] after 12 months). After two years this hair count was maintained and slightly increased (by an average of 138 hairs over placebo). Most men experienced a slow decline in hair count following the initial improvement; however, hair count was maintained above baseline throughout the 5 years of the studies. Hair loss continued in those men who were assigned a placebo tablet, such that the difference in hair count was 277 hairs at the end of the 5-year study period.
  • Finasteride does not affect body levels of cortisol, thyroid hormones, cholesterol, or bone mineral density.
  • No dosage adjustment is needed in men with kidney disease; however, finasteride must be used with caution in men with liver disease.
  • No clinically significant interactions have been reported.
  • Does not cause drowsiness.
  • Generic finasteride is available.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Sexual dysfunction (including decreased libido, erectile dysfunction, and ejaculation disorders) has occasionally been reported in men taking finasteride. Side effects are generally uncommon and do not result in drug discontinuation.
  • Breast cancer has been reported in men receiving finasteride in clinical trials and post-marketing surveillance but it is not known if there is an association with finasteride use because some men receiving placebo tablets in clinical trials also developed breast cancer.
  • Finasteride tablets are not approved for the prevention of prostate cancer. The use of finasteride tablets increases the risk of developing high-grade prostate cancer in men older than 55 years.
  • May not be suitable for some people such as those with obstructive uropathy,
  • May cause birth defects, most notably in a male fetus, if used during pregnancy (finasteride has not been proven to be effective in women anyway). Because of the potential for absorption through the skin, pregnant women and women who may be pregnant should avoid direct contact with broken or crushed tablets. If contact occurs, the area should be washed with soap and water immediately.
  • Has not been studied in people with liver disease; however, it is extensively metabolized via the liver.
  • May cause decreases in serum prostate-specific antigen (PSA) which should be taken into account in men with cancer whose PSA levels are being monitored. Reductions in PSA levels of about 50% have been reported in older men.
  • Finasteride may not be effective for bitemporal recession (often referred to as the "widow's peak").
  • Finasteride tablets should not be used in women with hair loss. No improvement in hair count, or patient or investigator assessment was noted in 137 postmenopausal women with androgenetic alopecia treated with finasteride tablets for 12 months. Finasteride should also not be given to children.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

Finasteride 5mg is effective at treating the symptoms and delaying the progression of BPH. Finasteride 1mg temporarily reverses hair loss in men with androgenetic alopecia (male pattern baldness). Sexual dysfunction has been reported in less than 10% of men who take finasteride.

5. Tips

  • Finasteride may be administered with or without meals. The usual dose is one tablet daily.
  • Daily use of finasteride 1mg for at least three months may be required before a benefit is seen with regards to regrowth of hair.
  • Finasteride tablets must be taken daily to maintain hair regrowth. Most men experience the biggest hair regrowth in the first two years of taking finasteride. Withdrawal of treatment leads to a reversal of hair gain within 12 months. Re-evaluate benefits of finasteride periodically.
  • Men should report any changes in their breast tissue such as lumps, pain, tenderness, enlargement, or nipple discharge.
  • Always read the patient package insert before starting finasteride and each time your prescription is renewed.
  • Finasteride tablets are for MEN only and should not be used by women or children.
  • Tell your doctor you are taking finasteride if your PSA levels are being monitored.

6. Response and effectiveness

  • A single oral dose of finasteride produces a rapid decrease in serum DHT concentrations, with the maximum effect observed within 8 hours. DHT suppression is maintained for at least 24 hours with continued treatment.
  • The daily dosing of finasteride 5mg tablets for up to 4 years reduced serum DHT concentrations by approximately 70%. Circulating levels of testosterone increased by approximately 10 to 20% but remained within the normal physiologic range.
  • Effects on hair regrowth may take up to three months to be seen. Effects do not persist once finasteride has been discontinued.

7. Interactions

Medicines that interact with finasteride may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with finasteride. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

There are no known major drug interactions with finasteride. Common medications that may have a moderate interaction with finasteride include:

  • antifungals, such as itraconazole or fluconazole
  • fluvoxamine
  • ginseng
  • HIV medications, such as nelfinavir or saquinavir
  • nefazodone
  • sirolimus or tacrolimus
  • terazosin
  • voriconazole.

Extensively metabolized by CYP3A4 enzymes but does not affect CYP isoenzymes.

May interfere with PSA tests. A 50% decrease in serum PSA concentrations in those with BPH receiving 5mg finasteride daily, even if they do have prostate cancer.

Note that this list is not all-inclusive and includes only common medications that may interact with finasteride. You should refer to the prescribing information for finasteride for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use finasteride only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2022 Revision date: May 24, 2022.