How Finasteride Treats Male Pattern Hair Loss

Finasteride is a prescription tablet that treats male pattern hair loss by blocking the enzyme that turns testosterone into DHT, the hormone that shrinks scalp follicles.¹ The FDA approves it as Propecia for hair loss in men only.¹ In two-year trials, men taking finasteride kept 138 more hairs in a one-inch scalp circle than men on placebo.² Benefit usually takes three months or more and fades within 12 months of stopping.¹ A physician can track your results, PSA and side effects over that time.

How Finasteride Works on DHT

Finasteride blocks Type II 5-alpha reductase, an enzyme that converts testosterone into dihydrotestosterone (DHT).¹ Male pattern hair loss is androgen-dependent shrinking of scalp follicles, with scalp DHT implicated as a contributing cause.² The Propecia label notes that balding scalp contains miniaturized hair follicles and more DHT than scalp with full hair.¹

The drop in DHT is fast once you start. Serum DHT fell 65% within 24 hours of a single hair-loss-strength tablet.¹ In a 42-day biopsy study, scalp skin DHT fell 64.1% at the strength used in Propecia, versus 13.0% on placebo.³

The trials enrolled men with mild to moderate loss, so the evidence applies most directly to follicles that are still producing hair.¹ Your physician can judge from your pattern and history how closely you match that group.

FDA Approval and Who It Is For

The FDA approves finasteride for two different conditions, at two different strengths, so the product you are prescribed depends on which condition you are treating.

• Propecia treats male pattern hair loss (androgenetic alopecia) in men only. The label states that it is not indicated for women and that efficacy in bitemporal recession, the temple corners, has not been established.¹
• Proscar treats symptomatic benign prostatic hyperplasia (BPH), an enlarged prostate. It is approved to improve urinary symptoms and lower the risk of urinary retention and prostate surgery.⁵ Proscar is not approved to prevent prostate cancer.⁵

The registration trials enrolled men 18 to 41 with mild to moderate hair loss, and 88% were Caucasian.¹ If you are older or have more advanced loss, those trials describe your situation less directly. That is a point to raise with your physician before you start.

What the Trials Found on Hair Growth

The two main crown (vertex) trials enrolled 1,553 men and followed 1,215 of them into a second year.² At baseline, men averaged 876 hairs in a one-inch circle of balding crown. Finasteride produced 107 more hairs than placebo at one year and 138 more at two years.² Men on placebo kept losing hair over the same period.²

Five-year extension data in the label show the same direction. Hair counts peaked in the first two years and then declined slowly, while staying above baseline through year five. Because the placebo group declined faster, the gap grew to 277 hairs at five years, against only 15 men still on placebo.¹ At 12 months, 58% of men on placebo had further hair loss, compared with 14% of men on finasteride.¹

In those trials, finasteride slowed hair loss and added modest regrowth. Most men on finasteride in the trials held or gained hair count, while most men on placebo lost it. How far your loss has progressed when you start shapes what you can expect.

Timeline and What Happens When You Stop

Finasteride asks for your patience. The label states that daily use for three months or more is generally needed before you see benefit.¹ It also states that continued use is needed to sustain benefit, and that benefit should be re-evaluated periodically.¹

If you stop, the effect reverses. The label says withdrawal "leads to reversal of effect within 12 months."¹ In the extension trials, men switched to placebo after one year lost their gains by month 24.¹

Plan for finasteride as a long-term medicine. Agree on a review point with your physician so you both judge the result on photographs, rather than on week-to-week impressions in the mirror.

Side Effects, Including Sexual Side Effects

If you have side effects on finasteride, the label suggests they are most likely to be sexual: decreased libido, erectile dysfunction and ejaculation disorder.¹ In year one of the hair-loss trials, the rates were:

Overall, 3.8% of men on finasteride reported at least one of these effects, compared with 2.1% on placebo.¹ The effects resolved in men who stopped and in most of those who continued. Each fell to 0.3% or lower by the fifth year of treatment.¹

For a wider view of your risk, a 2019 meta-analysis pooled 15 randomized, placebo-controlled trials with 4,495 men treated for hair loss.⁴ It found a relative risk of 1.66 for sexual dysfunction with finasteride compared with placebo.⁴ The authors advised physicians to assess sexual function in men taking these drugs.⁴

You should also know about the label's postmarketing reports. These include sexual dysfunction that continued after stopping, male infertility or poor semen quality, breast tenderness or enlargement, male breast cancer, and depression with suicidal thoughts and behavior.¹ These reports were voluntary, so their frequency and a causal link cannot be reliably established.¹

Tell your physician about any change in sexual function, mood or breast tissue as soon as you notice it. If you are planning children, raise fertility before you start. The label lists male infertility among postmarketing reports, with semen quality improving in reported cases after stopping.¹

PSA and Prostate Monitoring

Finasteride lowers PSA, the prostate-specific antigen blood test used to screen for prostate cancer.¹ At the BPH strength, PSA fell by about 50% in older men.¹ At the hair-loss strength, mean PSA in men 18 to 41 fell from 0.7 to 0.5 ng/mL over 12 months.¹

That shift changes how your PSA result should be read. The label states that any confirmed PSA increase while on finasteride should be evaluated, even when the value still falls in the normal range for men not taking the drug.¹

You should also know the label carries a warning on high-grade prostate cancer. In the seven-year Prostate Cancer Prevention Trial, men 55 and older taking the BPH strength had more Gleason 8 to 10 tumors, 1.8% versus 1.1% on placebo.¹ If you have PSA testing, make sure whoever reads it knows you take finasteride.

Finasteride, Women and Pregnancy

Finasteride is contraindicated in women who are or may become pregnant.¹ Blocking DHT can cause abnormal development of the genitals in a male fetus.¹

The label also states that a pregnant woman should not handle crushed or broken tablets. Intact coated tablets prevent contact during normal handling.¹ If you live with a partner who is or may become pregnant, keep your tablets whole and in their packaging.

Alternatives and Combination Options

You have several options for male pattern hair loss beyond finasteride. A 2025 Canadian expert consensus recommended seven interventions, including oral finasteride, topical finasteride, topical minoxidil, oral minoxidil, oral dutasteride, platelet-rich plasma and microneedling.⁶ A consensus recommendation is not an FDA approval, and only some of those options carry a hair-loss indication.

You can buy topical minoxidil without a prescription to regrow hair on the top of the scalp.⁷ Its Drug Facts label states that results may take at least four months and that hair loss resumes if you stop.⁷ The finasteride vs minoxidil page compares the two directly, and finasteride vs dutasteride covers the stronger enzyme blocker. A ketoconazole shampoo is sometimes added alongside these treatments.

If you want to avoid a daily tablet, topical finasteride and oral minoxidil each have their own page. Your physician picks the combination from your pattern, side-effect history and goals.

The Opt Take on Finasteride

Finasteride is a long-term medicine, and the effects you need watched show up over months, in libido, erections, mood and PSA. Every lab we order gets read by a physician before anyone is offered a treatment. You start with a 55+ biomarker panel that spans hormones, inflammation and cardiovascular risk, then a 1:1 review with an Opt Health physician.

If finasteride fits your plan, prescriptions ship from our pharmacy to your home. Your hair loss may also have causes beyond DHT, and what causes hair loss and male pattern baldness cover them. The hair loss protocol describes the approach. Labs and a physician consultation repeat every 3 to 4 months, so your physician can review your hair progress, ask about sexual function and mood, and adjust the plan on what your results did.

Get started: Begin with Opt Health, where a physician reads your labs, builds your plan, and adjusts it over the loop.

Frequently Asked Questions

This content is for informational purposes and does not replace evaluation, diagnosis, or treatment by a qualified medical professional.