Finasteride for Hair Loss: How It Works and What to Expect

Reviewed by LPMD Medical Group cliniciansUpdated 2026-09-135 min read

The short answer

Finasteride 1 mg once daily blocks the type II 5-alpha reductase enzyme, lowering the DHT that shrinks genetically sensitive hair follicles. In the label's trials it stopped further loss in most men and increased hair counts, with benefit usually visible after 3 to 6 months and building through 12 months. It works only while you take it, and it carries known sexual, mood and breast side effects to weigh with a clinician.

Finasteride is the medicine that launched a thousand forum threads. Somewhere online right now, a man is typing a 4,000-word post about how one pill ruined his life, directly beneath a man who has taken it for fifteen years and forgot it was a drug. Both are certain. Neither is your clinician.

Here is what the label, the trials and the professional societies actually say. We take the medicine seriously, which means taking the side effects seriously, without the sound effects.

Key facts

Finasteride 1 mg once daily is FDA-approved for male pattern hair loss in men only ¹.
It blocks type II 5-alpha reductase, cutting serum DHT by about 65 percent within 24 hours and lowering DHT in the scalp ¹.
In the label’s crown studies, 86 percent of men on finasteride had no further loss at one year versus 42 percent on placebo ¹.
Benefit takes at least 3 months to appear, and stopping reverses it within about 12 months ¹³.
Sexual side effects were reported by about 1 to 2 percent of men in the trials; depression, suicidal thoughts and persistent sexual dysfunction have been reported since ¹².
Anyone who is or may become pregnant should never handle crushed or broken tablets ¹.

How does finasteride work for hair loss?

Finasteride blocks type II 5-alpha reductase, the enzyme that converts testosterone into dihydrotestosterone (DHT) ¹. That enzyme sits in the prostate, seminal vesicles, epididymides and hair follicles, and in men with male pattern hair loss the balding scalp contains miniaturized follicles and more DHT than hairy scalp ¹. Less DHT at the follicle means less of the shrinking that turns thick hair into fuzz.

A single 1 mg tablet lowers serum DHT by about 65 percent within 24 hours, and daily dosing lowers scalp DHT as well ¹. The approved dose is 1 mg once a day, with or without food ¹. The studies enrolled men aged 18 to 41 with mild to moderate crown and mid-scalp loss; efficacy for temple recession has not been established ².

How long does finasteride take to work?

At least three months, and often closer to six before the mirror agrees ¹³⁴. The label is blunt: daily use for three months or more is necessary before benefit is observed, and MedlinePlus adds that improvement should continue through the first 12 months ¹³.

The label’s crown studies give the clearest numbers. At 12 months, 86 percent of men on finasteride had no further hair loss versus 42 percent on placebo; at 2 years, 83 versus 28 percent. Hair counts in a one-inch circle ran 107 hairs above placebo at 1 year, 138 at 2 years and 277 at 5 years ¹. The AAD’s summary: slows further loss in about 80 to 90 percent of men ⁴.

Checkpoint	What the evidence says
3 months	Earliest point benefit may appear; daily use for at least 3 months is required ¹³
6 months	When the AAD says results typically become visible ⁴
12 months	86% no further loss vs 42% on placebo; +107 hairs vs placebo ¹
2 years	83% no further loss vs 28% on placebo; +138 hairs ¹
5 years	+277 hairs vs placebo ¹
After stopping	Effect reverses within about 12 months ¹³

This is why we ask for Trail Marker photos at months 0, 6 and 12. Your mirror is a terrible scientist.

What happens when you stop taking finasteride?

DHT comes back, and so does the pattern. The label says the effect reverses within 12 months of stopping, and MedlinePlus says you will probably lose any regrown hair during the first year after you stop ¹³. Finasteride is a Maintenance Mode medicine: it holds the line while you take it.

What are the side effects of finasteride?

In the one-year trials, sexual side effects were reported by a small minority of men, and by some on placebo too: decreased libido in 1.8 percent versus 1.3 percent, erectile dysfunction in 1.3 versus 0.7 percent, and ejaculation disorder in 1.2 versus 0.7 percent ¹². Testicular pain has also been reported ³.

After the drug reached the market, further reports emerged that the trials did not measure, so their frequency is unknown: depression and suicidal ideation and behavior; sexual dysfunction that continued after stopping, including erectile, libido, ejaculation and orgasm problems; breast tenderness and enlargement; male breast cancer; and hypersensitivity reactions including rash, hives and swelling of the lips and face ¹²³. MedlinePlus also lists an increased risk of high-grade prostate cancer ³. We unpack these numbers in our side-effects article. The short version: uncommon, real, and worth a conversation rather than a shrug.

What are the pregnancy and PSA warnings?

Two warnings that never get enough airtime. First, finasteride can harm a male fetus, so anyone who is or may become pregnant should not handle crushed or broken tablets ¹³. Intact tablets are coated to prevent contact during normal handling, so the rule is simple: do not split or crush tablets, and do not leave broken ones around ¹. The label reports finasteride in semen at very low or undetectable levels ¹.

Second, finasteride lowers PSA, the blood test used in prostate cancer screening. Any confirmed rise from your lowest value on finasteride should be evaluated even if it is still in the normal range, so any clinician ordering a PSA needs to know you take it ¹².

Is generic finasteride the same as compounded finasteride?

Generic finasteride 1 mg tablets are FDA-approved and usually the least expensive option at any pharmacy. Compounded finasteride, whether a topical, an unusual strength or a combination with minoxidil, is prepared by a compounding pharmacy and is not FDA-approved, so FDA does not review its safety, effectiveness or quality before sale ⁶. In April 2025, FDA warned that men using compounded topical finasteride reported side effects like those of the pill, and some had been told there was no risk because the product was topical ⁷. There are reasonable cases for a compounded product; “no side effects” is not among them. See the finasteride page for how we prescribe it.

When to talk to a clinician

Stop and call if you notice breast lumps, pain, nipple discharge or enlargement; low mood, hopelessness or thoughts of harming yourself; rash, hives or swelling of the face or lips; or testicular pain ¹³. Suicidal thoughts are an emergency: call or text 988 in the US. Sexual side effects deserve a call too; there are Re-route options, including a different medicine or stopping.

Also check in if you are over 60, since the medicine may be less effective ⁵, if a PSA test is coming up, or if your hair loss is patchy, sudden or itchy.

Bring your questions, family photos and forum screenshots to a $45 consult. We have read the threads. We would rather read your chart.

Hairy questions, straight answers

How long does finasteride take to work for hair loss?

The label says daily use for at least three months is needed before any benefit is seen, and most men are told to judge results at six to twelve months. In the label's trials, 86 percent of men had no further hair loss at one year, and hair counts kept improving through year two.

Do you have to take finasteride forever?

You have to take it for as long as you want the benefit. The label says the effect reverses within about 12 months of stopping, and MedlinePlus says you will probably lose any hair that regrew during the first year after you stop. It is a maintenance medicine.

What percentage of men get sexual side effects from finasteride?

In the one-year trials, decreased libido was reported by 1.8 percent of men on finasteride versus 1.3 percent on placebo, erectile dysfunction by 1.3 versus 0.7 percent, and ejaculation problems by 1.2 versus 0.7 percent. After marketing, some men reported sexual dysfunction that continued after stopping; how often that happens is not known.

Can finasteride cause depression?

Depression and suicidal ideation and behavior have been reported in men taking finasteride since it reached the market, and the label now lists them. The frequency is not established. If your mood drops or you have thoughts of harming yourself while taking it, stop and contact a clinician; suicidal thoughts are an emergency.

Is it safe for my partner if I take finasteride?

Intact tablets are coated and safe to be around. The risk is to a male fetus, so anyone who is or may become pregnant should never handle crushed or broken tablets. The label reports finasteride in semen at very low or undetectable levels.

Does finasteride affect PSA tests?

Yes. Finasteride lowers PSA, the blood test used in prostate cancer screening. Any confirmed rise from your lowest value while on the drug should be evaluated even if it is still in the normal range, so tell any clinician who orders a PSA that you take finasteride.

Sources

Information checked 2026-09-13 by LPMD Medical Group clinicians. This article is general education, not a diagnosis or a treatment plan for you. Your clinician and pharmacist provide the instructions for your actual prescription.