Finasteride is a daily pill that lowers DHT, the more potent androgen that drives male pattern hair loss and benign prostate enlargement. It blocks the enzyme that converts testosterone to DHT, so circulating and scalp DHT drop by roughly 60-70% on the 1 mg dose used for hair, and over 90% on the 5 mg dose used for the prostate. The hair follicles that were being slowly miniaturised by DHT stop shrinking and, in most users, partially recover.

Most people take it because they're losing their hair, they want to keep it, and finasteride is the single intervention with the strongest long-term evidence in men. It is the closest thing to a "keep your hair" pill that exists. The trade-off is that it works systemically, lowering DHT everywhere in the body, which is where the well-known concerns about libido, mood, and sexual function come from. The vast majority of users have no significant side effects, but a meaningful minority do, and for a smaller subset those side effects persist after stopping.

The last point has a name, post-finasteride syndrome (PFS), and it's the reason this drug needs more thought than the average prescription. A small fraction of users report sexual, mood, and cognitive symptoms that continue for months or years after stopping the drug. The medical community is split on how to characterise it, the absolute risk is low (well under 1% in cohort data), and there's no reliable predictor of who develops it. It doesn't make finasteride a bad drug, but it does make it one you should understand before you start, not after.

Deep-dive

Dosage:

• Standard hair loss dose: 1 mg/day, oral, once daily, at any time of day with or without food. This is the dose with the strongest evidence and the one most users land on. Half-life is short (6-8 hours) but the enzyme inhibition lasts much longer, which is why once-daily dosing works
• Microdosing (0.25-0.5 mg/day, or 1 mg every other day): Reasonable alternative for users who want most of the benefit with potentially fewer side effects. The dose-response curve plateaus relatively quickly, 0.2 mg/day reduces scalp DHT around 50% versus the 60-65% at 1 mg/day. Real-world experience suggests microdosing maintains most of the hair benefit, but the long-term controlled trial data is thin
• BPH dose: 5 mg/day, oral. This is the dose for prostate enlargement and is overkill for hair loss. It doesn't produce meaningfully more hair benefit than 1 mg, but it does increase systemic side effect risk
• Topical finasteride 0.25% solution: 100-200 µL applied to the scalp once daily, delivering roughly 0.25-0.5 mg of finasteride directly to the scalp. Produces scalp DHT reduction comparable to oral with around 60-70% lower serum DHT impact. Apply to clean, dry scalp, let it absorb for 10 minutes before lying down or applying minoxidil. Reasonable choice for users who want to minimise systemic exposure
• Female dosing: 2.5-5 mg/day oral for premenopausal women (off-label, requires reliable contraception); 1 mg/day showed no benefit in postmenopausal women in the only large trial, but 2.5-5 mg has shown signal in observational cohorts. Topical 0.5% solution daily is a reasonable choice in postmenopausal women specifically. Do not use in pregnancy or while trying to conceive, this is non-negotiable
• Timing: No clinically meaningful difference between morning and evening dosing. Pick the time you're most likely to take it consistently, that's the variable that matters
• Onset and assessment window: Expect no visible change in the first 3 months. By month 6 hair shedding usually slows and existing hair starts to thicken. By month 12 photo comparisons typically show stabilisation or modest regrowth. Don't judge before 12 months. If after 12-18 months of consistent daily use there's no improvement on photos, you're a non-responder and switching to dutasteride is a reasonable next step
• Discontinuation: Whatever hair you've kept or regrown will be lost within 6-12 months of stopping, the underlying genetics take over again. This is a long-term commitment by nature of the disease, not the drug. If you're not prepared to take a daily pill for years, the cost-benefit doesn't favour starting
• Stacks: Pairs naturally with topical or low-dose oral minoxidil, the two mechanisms are complementary and the combination consistently outperforms monotherapy. Red light therapy is a reasonable third addition. Ketoconazole 2% shampoo a few times per week adds a small local anti-androgen and anti-inflammatory effect. Stacking with RU58841 is overkill for most users

Here's what you can expect:

The first 3-4 months are usually uneventful or feature an initial shed as follicles cycle from telogen back into anagen. Don't quit during this phase, it resolves and is a positive sign that follicles are responding. By month 6, hair shedding noticeably slows and existing hair feels thicker. By month 12, photo comparison under consistent lighting typically shows clear stabilisation and partial regrowth in the crown and mid-scalp. Frontal hairline gains are usually more modest. By year 2-3, the benefit plateaus and the rest of the work is maintenance.

Subjective experience for most users is unremarkable: no on-drug sensation, no day-to-day cognitive or sexual change, just the gradual realisation a year in that you're not seeing more scalp through your hair in photos. A minority will notice sexual side effects in the first weeks to months (lower libido, softer erections, smaller ejaculation volume). These resolve in most cases either with continued use or after stopping. A smaller minority will notice mood changes, low motivation, or cognitive flatness. Don't push through these, stop the drug, reassess at 4-8 weeks off, and make the decision again with that information.

If you stop, expect to lose all of the regrowth and most of the maintained hair within 12 months. This isn't the drug withdrawing, it's the underlying genetics expressing themselves now that the brake is off.