Finasteride for Hair Loss: How It Works, Side Effects, Dosage and Results

What is finasteride and how does it work?

Finasteride is a prescription-only medicine that slows hereditary hair loss in men by lowering DHT, the follicle-damaging hormone. Pharmacologically, finasteride is a 4-azasteroid and a selective inhibitor of type II 5-alpha-reductase. Its effect relies on blocking this enzyme, which converts testosterone into the considerably stronger dihydrotestosterone (DHT). According to the Propecia SmPC (Organon, as of August 2024), its selectivity for the type II isoform is more than 100 times higher than for type I.

Finasteride at a glance

DHT is the central driver of androgenetic alopecia. Balding scalp skin contains raised levels of DHT, and the hormone shortens the growth phase (anagen) of genetically sensitive follicles. With each cycle the hairs become thinner and shorter, a process known as miniaturisation. Finasteride acts at precisely this root cause.

How strongly finasteride lowers DHT was shown by the dose-finding study by Roberts and colleagues (1999): at 1 mg daily, the serum DHT level fell by 71.4 per cent, and by 64.1 per cent on the scalp itself. The dose-response curve flattens out early: even 0.2 mg achieved most of the maximum possible reduction, and 5 mg added barely anything more.

That is precisely why 1 mg is the standard dose for hair loss. Finasteride works systemically, that is, throughout the whole body, in contrast to topical finasteride (more on that below) and to minoxidil, which acts purely locally and without any hormonal effect. To understand how the hair cycle works, with its anagen, catagen and telogen phases, see the article on the hair cycle.

How well does finasteride work against hair loss?

Finasteride for hair loss stops or slows hereditary hair loss in the majority of men, and some achieve visible regrowth. The evidence base is three randomised, placebo-controlled phase III trials involving 1,879 men aged 18 to 41 (Propecia SmPC, section 5.1). The key five-year figures:

• ✓Stabilisation: in 90 per cent (global photographic assessment) or 93 per cent (investigators), hair loss remained stable over five years.
• ✓Regrowth: an increase in hair growth was seen in 65 per cent (hair count), 48 per cent (expert panel) and 77 per cent (investigators).
• ✓Hair counts: after 2 years +88 hairs, after 5 years still +38 hairs per measured area, compared with -239 hairs on placebo after 5 years.

Kaufman and colleagues (2008) confirmed this independently: over five years, finasteride 1 mg reduced the risk of further visible hair loss compared with placebo by 93 per cent (95 per cent confidence interval 89 to 97, p less than 0.001). One caveat is that the number of men in the placebo group became small over the years. Even so, the trend in favour of finasteride is clear and has been shown repeatedly.

You have to stay honest about where it works. The effect is documented above all on the top of the scalp and in the crown area (vertex). For the bitemporal recession of the hairline, that is, the classic receding temples, and for end-stage hair loss, the SmPC states explicitly that no efficacy was demonstrated. Finasteride has no effect on follicles that are already completely lost: it does not make bald areas grow back.

That is why expectations have to match the stage. The Hamilton-Norwood scale helps to put the realistic benefit into perspective: the earlier the hair loss, the more can be preserved. With extensive baldness the medicine achieves next to nothing.

Realistic finasteride expectations by Norwood stage

A rough guide, not a prediction for the individual case. Assessing the stage and choosing the treatment belongs in the hands of a doctor.

How quickly does finasteride work? The timeline

How quickly finasteride works depends on the slow hair cycle: according to the SmPC, first signs of stabilisation are generally not expected until after 3 to 6 months of continuous use. The improvements in hair count were greatest after about 2 years and then slowly declined again, but remained clearly better than on placebo up to year 5.

Individual courses vary. A lack of effect after 12 months should be discussed with a doctor.

A word on personal accounts and on what is known as initial shedding. Unlike with minoxidil, where an initial shedding phase is well documented, the SmPC does not list initial shedding as a separate side effect for finasteride. It is occasionally described in forums and personal reports, but it is not consistently documented and should not be equated with the better-documented minoxidil shedding.

Something else that shapes experiences with finasteride: those who start late or have a high Norwood stage less often experience visible regrowth and more often see preservation. That matches the trial data and is not a bad outcome, but simply the realistic expectation. Individual reports are no substitute for medical follow-up.

Taking finasteride correctly: the dosage

The finasteride dose for hair loss is 1 mg daily, with or without food, ideally at the same time of day. Oral bioavailability is around 80 per cent and is not affected by food (SmPC, section 4.2). Important: according to the SmPC, a higher dose is not more effective, because the reduction in DHT is already almost maximal at 1 mg.

The difference between 1 mg and 5 mg is therefore clear: the 5 mg tablet (such as Proscar) is licensed for benign prostatic enlargement, not for hair. Quartering it on your own or increasing the dose yourself is not a sensible route. In any case, the effect only exists with continuous use; a one-off course achieves nothing.

The subject of microdosing often comes up, meaning lower doses or taking it every other day to reduce side effects. In theory this can be inferred from the flat dose-response curve, but there is no controlled study comparing such a regimen with the daily 1 mg dose using hair-growth endpoints. It remains an off-label approach to be supervised by a doctor, not a standard therapy.

How do I get a finasteride prescription?

In the UK you can only obtain finasteride through a doctor or prescriber, because the active ingredient is prescription-only (SmPC, section 11). The first points of contact are your GP, a dermatologist or a urologist. The doctor makes the diagnosis, explains the benefits and risks, and prescribes finasteride if you are suitable.

Alongside this, reputable telemedicine providers offer an online prescription. After a medical questionnaire or a video consultation, a registered doctor issues the prescription, and the medicine comes via an online pharmacy. This route is legal, as long as a doctor is genuinely involved and you are informed about the risks, including the warnings on mood and suicidal thoughts flagged in the 2025 safety alert.

What does finasteride cost? Originator, generics and the NHS

As a generic, finasteride costs roughly between £15 and £30 per month as of 2026, depending on the provider and pack size; the originator product Propecia costs considerably more. Because finasteride for hair loss is not covered by the NHS, patients pay this amount themselves.

The active ingredient is identical in the originator and the generic. Since the patent expired there have been numerous 1 mg generics that contain the same active ingredient at the same dose and are usually many times cheaper than the originator Propecia. Medically, there is no difference in effect between the originator and an officially approved generic. Price is therefore the main argument for a generic.

The NHS does not fund finasteride for hair loss, even with a prescription. The reason: it is classed as a cosmetic (lifestyle) treatment rather than a medical necessity. For the prostate indication (5 mg) the funding position can be different, but that does not apply to hair-loss treatment.

Topical finasteride: an alternative you apply to the scalp?

Topical finasteride is applied directly to the scalp as a solution or spray and is intended to lower DHT locally, with less systemic exposure. In Europe it is no longer just a compounding grey area: with Finjuve (2.275 mg/ml spray, made by Almirall) there is a licensed finished medicine, applied once daily with 1 to 4 sprays in men aged 18 to 41.

Alongside this, individually compounded pharmacy formulations still exist, such as a 0.15 per cent finasteride solution, often combined with minoxidil. These have not gone through their own registration study. The rationale for topical finasteride is a smaller reduction in blood DHT and therefore potentially fewer systemic side effects. The long-term evidence, however, is thinner than for the oral preparation.

Does finasteride distort the PSA value?

Yes, finasteride lowers the PSA value, the most important blood marker in prostate-cancer screening. The SmPC states the practical rule verbatim: “A doubling of the PSA value should be considered in men taking Propecia before this test result is assessed.” Anyone taking finasteride must therefore inform every doctor treating them.

Specifically, the mean PSA in the studies of young men fell from 0.7 to 0.5 ng/ml after 12 months. The widespread rule of thumb of a halving comes from studies in older men on the 5 mg dose. It therefore makes sense to have a baseline PSA measured before starting treatment, so that later checks are interpreted correctly.

A common misunderstanding concerns the risk of prostate cancer. The often-cited PCPT study investigated 5 mg finasteride in men over 55 for cancer prevention, not the 1 mg hair-loss indication. There, the overall rate of prostate carcinomas fell by 24.1 per cent, while the proportion of higher-grade tumours was slightly higher. Transferring these data to the hair-loss treatment of young men would be misleading. To find out what a sensible blood test for hair loss looks like, see the separate article.

What side effects does finasteride have?

The most common finasteride side effects affect sexual function: reduced libido, erectile and ejaculation disorders. According to the SmPC, sexual side effects occurred in the first year in 3.8 per cent of finasteride users compared with 2.1 per cent on placebo. Over the following four years the frequency fell to 0.6 per cent. About 1 per cent stopped treatment for this reason in the first year.

• •Sexual side effects are mostly reversible and decrease over the course of treatment.
• •Depression is listed as “uncommon”, but in the randomised studies there was no difference from placebo.
• •Lumps, pain or discharge from the breast should be checked by a doctor promptly (rare reports of breast cancer in men).

Frequency categories in the SmPC: uncommon = 1 to 10 per 1,000, “not known” = cannot be estimated from the available data (spontaneous reports). No substitute for a medical consultation.

Balance matters here: finasteride is neither harmless nor does it “guarantee impotence”. Most men tolerate it, a meaningful proportion do notice sexual side effects, which mostly resolve after stopping. The potential for interactions with other medicines is low according to the SmPC (metabolised via CYP3A4), but a medical discussion before starting remains a must.

Post-finasteride syndrome and psychological effects: what is established?

Post-finasteride syndrome (PFS) is the term for sexual, physical and psychological complaints that are said to persist after stopping finasteride. Whether finasteride causally triggers these complaints has not been conclusively established scientifically. The authorities take the reports seriously, but a straightforward proof of causation is still lacking to this day (as of 2026).

Regulation has tightened step by step. In 2012 the US authority FDA added notes on sexual dysfunction that can persist after stopping. In 2017 the EMA added a warning about mood changes including depression and, more rarely, suicidal thoughts, and assessed a causal link as “at least a plausible possibility”.

The most recent and most important piece of evidence is the safety alert issued in 2025 following an EU-wide review. That review identified 325 relevant cases of suicidal thoughts in the EudraVigilance database, dated 15 September 2025. In future, 1 mg packs will include a patient card. At the same time, the committee concluded that the benefit of finasteride continues to outweigh the risks.

Scientifically, PFS as a distinct condition is contested. A survey of Spanish dermatologists (2025) found that 98.1 per cent consider PFS to be more likely psychiatric or driven by a nocebo effect. Other, mechanistically oriented studies, by contrast, report measurable biological differences. Neither “PFS is proven” nor “PFS is pure imagination” is scientifically tenable.

Stopping finasteride: what happens then?

If you stop finasteride, DHT rises again and hereditary hair loss continues. According to the SmPC, the effects reverse within 6 months, and after 9 to 12 months the original, untreated state is reached again. The hair maintained by the therapy is lost over this period.

From this follows a central consequence for the decision: finasteride is a long-term therapy, not a one-off course. Anyone who wants to keep the result takes it continuously. Stopping should be done in consultation with a doctor, especially if the reason is side effects, so that alternatives can be considered together.

Can women take finasteride?

Finasteride is contraindicated for women of childbearing age. Because it inhibits the formation of DHT, if taken by a pregnant woman it can lead to malformations of the external genitalia of male foetuses (teratogenicity). Women who are pregnant or potentially pregnant must not even touch broken or crushed tablets, because of the possible absorption through the skin.

An often-overlooked figure also belongs to the topic of finasteride and women: in postmenopausal women with androgenetic alopecia treated for 12 months with finasteride 1 mg, no efficacy could be demonstrated according to the registration study. A Cochrane review rates the evidence in women overall as insufficient.

In women, moreover, diffuse hair loss often has other causes, such as iron deficiency or a thyroid disorder. Before any discussion of an active ingredient, therefore, comes the investigation of the cause. More on this in the article on hair loss in women, and on hormones in the article on hormones and hair.

Finasteride, minoxidil or dutasteride?

Finasteride, minoxidil and dutasteride act at different points: finasteride and dutasteride lower DHT (the cause), while minoxidil prolongs the growth phase locally, without any hormonal effect. The European S3 guideline on androgenetic alopecia (EDF, Kanti and colleagues 2018) lists topical minoxidil 5 per cent and oral finasteride 1 mg as therapies with a high level of evidence.

• •Combination: a meta-analysis of 7 randomised studies (n=396) found the combination of minoxidil and finasteride more effective than either monotherapy.
• •Dutasteride: inhibits both enzyme types and lowers DHT more strongly (about 90 to 93 per cent), but it is only licensed for the prostate. Its use for hair loss is off-label.

The comparison is factual, not a treatment recommendation. Which option or combination fits depends on the stage, the age and individual tolerability, and belongs to a medical discussion. Another, newer active ingredient is topical clascoterone, which blocks DHT locally at the follicle and is described in the article on clascoterone.

Diffuse or genetic? When finasteride is the wrong approach

Finasteride works exclusively against androgenetic, that is, hereditary hair loss, recognisable by the pattern with receding temples and a thinning top of the scalp or crown. Diffuse hair loss across the whole head due to iron deficiency, a thyroid disorder or other causes does not respond to finasteride. Here the cause should be investigated first, and often both forms occur at the same time.

That is why it is worth looking at the pattern. Diffuse thinning without a clear pattern points more towards telogen effluvium, for example due to an iron deficiency or a thyroid disorder. A look at the causes of hair loss and at the article on androgenetic alopecia helps with the assessment.

This is exactly where a hair analysis comes in. It clarifies which type is present before any decision about treatment is made. In advanced androgenetic alopecia with follicles that are already lost, finasteride can stabilise the existing hair, but cannot make bald areas grow back. For such areas, a hair transplant (FUE extraction plus DHI implantation) is the established, permanent option, because it transplants DHT-resistant hair from the back of the head.

Medicine and transplant are not mutually exclusive here. Accompanying medical maintenance is common practice to protect the non-transplanted, still DHT-sensitive native hair while the transplanted hair stays put. Elithair’s free hair analysis is a visual pattern analysis and helps to distinguish the genetic type from the diffuse type. It is no substitute for a medical blood test, which you should always have carried out if a deficiency is suspected.

Conclusion: finasteride at a glance (as of 2026)

Finasteride is the most effective oral standard therapy against hereditary hair loss in men, and in the registration trials it stabilised around 90 per cent of users over five years. It is a long-term therapy, works only on the androgenetic pattern and above all on the top of the scalp, and the effect ends when it is stopped.

At the same time, it is a medicine that carries real side effects, from sexual dysfunction to the warnings on mood and suicidal thoughts confirmed in the 2025 safety alert. The benefit and the risk can only be weighed up individually and with a doctor, especially where there is a wish to have children, a psychiatric history or problems with tolerability. The first step always remains a clean diagnosis.

Frequently asked questions about finasteride

Scientific sources