Finasteride is a prescription medication with two primary uses: treating male pattern hair loss and managing an enlarged prostate. It works by blocking the conversion of testosterone into a more potent hormone called dihydrotestosterone (DHT), which drives both scalp hair thinning and prostate growth. The drug comes in two dosages, each tied to a specific condition, and it’s also used off-label for a handful of other purposes.
Male Pattern Hair Loss
The 1 mg daily dose, sold under the brand name Propecia, is approved for treating male pattern hair loss (androgenetic alopecia) in men only. DHT shrinks hair follicles over time, gradually producing thinner, shorter hairs until the follicle stops producing visible hair altogether. By lowering DHT levels in the bloodstream, finasteride allows weakened follicles to recover and resume normal hair production.
Results aren’t immediate. During the first one to three months, DHT levels drop and follicles begin regaining their normal size, but you’re unlikely to see visible changes. Between three and six months, many people notice their hairline has stopped receding or that thinning areas look slightly thicker. By six months to a year, the improvements become more obvious: thicker hair, less shedding, and in some cases regrowth in areas that had thinned significantly. Full effects typically take about 12 months of consistent daily use.
The catch is that finasteride only works as long as you take it. If you stop, DHT levels climb back to their previous levels over four to six months, and hair loss gradually resumes.
Enlarged Prostate (BPH)
The 5 mg daily dose, sold as Proscar, treats benign prostatic hyperplasia, a condition where the prostate gland grows large enough to compress the urethra and interfere with urination. Symptoms include a weak urine stream, frequent nighttime urination, and difficulty fully emptying the bladder. Because DHT is a major driver of prostate growth, blocking it with finasteride can shrink the gland and relieve these symptoms over time.
In clinical trials, finasteride was most effective for men whose prostates had already grown past a certain size. Among men with a baseline prostate volume of 30 milliliters or greater, 88% of those on finasteride avoided progression of their symptoms over the study period, compared with about 78% on placebo. The benefit is less pronounced in men with smaller prostates. Like its use for hair loss, finasteride for BPH requires ongoing treatment; stopping the medication allows the prostate to resume growing.
One important note: finasteride lowers levels of prostate-specific antigen (PSA), a protein measured in routine prostate screening, by roughly 50%. If you’re taking finasteride and get a PSA test, your doctor needs to account for this reduction to interpret the results accurately.
Off-Label Use in Women
Finasteride is FDA-approved for men only, but it’s sometimes prescribed off-label for women dealing with hirsutism, which is excessive hair growth on the face and body often linked to conditions like polycystic ovary syndrome (PCOS). Because DHT stimulates body hair growth while simultaneously thinning scalp hair, blocking it can reduce unwanted facial and body hair in women as well.
Clinical studies comparing finasteride to placebo found meaningful improvements in hirsutism after six months of treatment, with no improvement in the placebo groups. Typical doses for women range from 2.5 to 5 mg daily, though higher doses produce more side effects including dry skin, reduced libido, headache, and bloating. Some evidence suggests that taking 2.5 mg intermittently rather than continuously produces similar results with fewer side effects.
Finasteride performs comparably to other anti-androgen treatments used for hirsutism. In head-to-head trials, spironolactone tended to produce equal or slightly better results, depending on the study. It’s not a first-line treatment for most women, but it’s a reasonable option when other approaches haven’t worked well enough.
Side Effects
The most discussed side effects are sexual in nature. In clinical trials, up to 15% of men taking the 5 mg dose for enlarged prostate reported issues like erectile dysfunction, decreased libido, or changes in ejaculation within the first year. Rates are generally lower at the 1 mg dose used for hair loss, though they still occur. For most men, these effects resolve after stopping the medication or sometimes even while continuing it.
A small subset of users report persistent sexual, physical, or psychological symptoms that last more than three months after stopping the drug, sometimes referred to as post-finasteride syndrome. A large retrospective study found that about 0.8% of patients developed sexual dysfunction while on finasteride, and among those, roughly one in three still had symptoms after discontinuation. The main risk factor for persistence was using the drug for longer than seven months. The condition was added to the National Institutes of Health’s list of rare diseases in 2015, and the FDA mandated that suicidal ideation be included on the product label in 2022.
The medical literature on why these persistent symptoms occur, how long they last, and how to treat them remains limited. For most people the medication is well tolerated, but it’s worth being aware of this possibility before starting treatment.
Pregnancy and Handling Precautions
Finasteride can interfere with the development of male genitalia in a developing fetus, which is why it carries a warning about use during pregnancy. The drug’s manufacturers have historically recommended that pregnant women avoid handling crushed or broken tablets, since the active ingredient can be absorbed through the skin. Intact tablets have a coating that prevents skin contact with the medication.
If your partner takes finasteride and you’re pregnant, the actual risk is very low. According to the NHS, most experts agree that the trace amounts potentially present in semen are not clinically significant, and condom use during pregnancy, while still recommended by the manufacturer, is not considered necessary by most specialists.
The Two Dosages at a Glance
- 1 mg daily (Propecia): Male pattern hair loss. Results visible in three to six months, full effect at 12 months.
- 5 mg daily (Proscar): Enlarged prostate (BPH). Most effective for men with prostate volume above 30 mL.
Some people prescribed the lower dose for hair loss choose to split a 5 mg tablet into quarters with a pill cutter to reduce cost, since the higher-dose version is often less expensive per milligram. This is a common practice, though tablet splitting can produce uneven doses.