Hormone Journal

Finasteride

Also known as: Propecia

Medically reviewed by Hormone Journal Editorial Team · Last reviewed 2026-05-22

Finasteride is a 5-alpha reductase inhibitor approved in Canada for male pattern hair loss (1 mg) and benign prostatic hyperplasia (5 mg), reducing scalp DHT by up to 70%.

What it is

Finasteride is a 5-alpha reductase inhibitor that reduces dihydrotestosterone (DHT) levels by up to 60–70%, and is approved in Canada for two indications: male pattern hair loss (androgenetic alopecia) at 1 mg daily (brand name Propecia) and benign prostatic hyperplasia (BPH) at 5 mg daily (brand name Proscar). Also known by its brand name Propecia for the hair-loss indication, finasteride is one of only two oral medications approved by Health Canada for androgenetic alopecia in men — the other being dutasteride in some provinces. Androgenetic alopecia affects roughly 50% of men by age 50, making finasteride one of the most commonly prescribed hormone-modulating drugs in Canadian men's health. The drug is available by prescription only and is listed on several provincial formularies for BPH, though coverage for the hair-loss indication varies by province.

Causes and mechanism

Finasteride works by blocking the enzyme 5-alpha reductase (specifically the type II isoenzyme), which converts testosterone into dihydrotestosterone (DHT) in the prostate, hair follicles, and skin. DHT is the primary androgen responsible for prostate growth and for the miniaturization of hair follicles that drives male pattern baldness. By inhibiting this conversion, finasteride raises circulating testosterone slightly while sharply lowering DHT — scalp DHT falls by approximately 64% and serum DHT by roughly 70% at the 1 mg dose. At the 5 mg dose used for BPH, prostate volume typically decreases by 20–30% over 6–12 months, reducing urinary obstruction.

The two approved indications differ mainly in dose, not mechanism:

IndicationDoseOnset of effectPrimary target
Androgenetic alopecia1 mg/day3–6 monthsScalp hair follicles
Benign prostatic hyperplasia5 mg/day3–6 months (symptoms); up to 12 months (volume)Prostate gland
Prostate cancer risk reduction (off-label)5 mg/dayStudied over 7 years (PCPT trial)Prostate epithelium

Symptoms and diagnosis

Finasteride is a treatment, not a condition — so there is no "diagnosis" of finasteride use. Clinicians prescribe it after confirming androgenetic alopecia (typically by clinical pattern assessment, sometimes with dermoscopy or trichoscopy) or BPH (confirmed by symptom scoring, digital rectal exam, and PSA testing). In Canada, LifeLabs and Dynacare both offer serum DHT and PSA panels that can help establish baseline values before starting therapy and monitor response.

Patients considering finasteride for hair loss should be aware that results require sustained use: hair count improvements are typically measurable at 12 months, and stopping the drug reverses gains within 6–12 months. For BPH, symptom relief may begin within weeks but full prostate volume reduction takes up to a year.

Treatment options

Finasteride is taken orally once daily. For hair loss, the 1 mg tablet (generic or Propecia) is taken continuously; for BPH, the 5 mg tablet (generic or Proscar) is often combined with an alpha-blocker such as tamsulosin for faster symptom relief. Generic finasteride is widely available in Canada and is substantially less expensive than branded versions.

Alternatives and adjuncts include:

  • Minoxidil (topical or oral) — can be used alongside finasteride for hair loss; acts through a different mechanism (vasodilation/follicle prolongation)
  • Dutasteride — inhibits both type I and type II 5-alpha reductase; not formally approved by Health Canada for hair loss but prescribed off-label
  • Alpha-blockers (tamsulosin, alfuzosin) — for BPH symptom relief without volume reduction
  • Surgical options (TURP, laser procedures) — for BPH refractory to medical therapy

Canadian patients can access finasteride prescriptions through in-person physicians, or through telehealth platforms such as Felix, Maple, Cleo, or Phoenix, which offer online consultations and prescription delivery.

When to see a clinician in Canada

See a physician or nurse practitioner if you notice progressive hair thinning at the crown or temples, or urinary symptoms such as weak stream, incomplete emptying, or nocturia. Before starting finasteride, a baseline PSA test is recommended — finasteride approximately halves PSA values, so any clinician ordering a PSA while you are on the drug must double the result to interpret it correctly against standard reference ranges. This is a well-documented clinical pitfall that Health Canada's product monograph addresses explicitly. Men with a family history of prostate cancer should discuss the nuanced risk-reduction data (the Prostate Cancer Prevention Trial showed a 25% relative reduction in prostate cancer incidence but a signal toward higher-grade tumours in the finasteride arm, though subsequent analyses have questioned whether this reflects detection bias). Women who are pregnant or may become pregnant must not handle crushed or broken finasteride tablets, as the drug causes genital birth defects in male fetuses.

Limitations and open questions

Research is still emerging on post-finasteride syndrome (PFS) — a contested condition in which a subset of men report persistent sexual dysfunction, depression, and cognitive symptoms after stopping the drug. The prevalence of PFS is not established; clinical trial rates of sexual side effects during treatment are approximately 3–4% (versus roughly 2% on placebo), but post-marketing reports suggest some effects persist beyond discontinuation in a small number of patients. Health Canada has issued label updates requiring disclosure of persistent sexual side effects, but has not issued formal clinical guidance on how to manage or diagnose PFS. The biological mechanism, if any, remains under investigation. Additionally, finasteride's role in prostate cancer prevention is not an approved indication in Canada, and the long-term cardiovascular and neurological effects of sustained DHT suppression are not fully characterized. Clinicians and patients should weigh these uncertainties explicitly before committing to long-term use.

FAQs

How is finasteride different from minoxidil for hair loss?

Finasteride works hormonally by blocking DHT production, while minoxidil works locally by widening blood vessels around hair follicles and prolonging the growth phase. Clinical trials show finasteride 1 mg produces greater hair count increases than topical minoxidil 2% when used alone, and the two can be combined for additive effect. Finasteride requires a prescription in Canada; minoxidil is available over the counter at most pharmacies.

Does finasteride affect PSA test results, and does that matter for prostate cancer screening?

Yes — finasteride at 5 mg reduces PSA values by approximately 50% after 6 months of use, and the 1 mg dose produces a smaller but still meaningful reduction. Any clinician interpreting a PSA result in a man on finasteride should double the measured value to compare it against standard reference ranges. Failing to account for this can mask a rising PSA that would otherwise prompt further investigation for prostate cancer.

Is finasteride covered by provincial drug plans in Canada?

Coverage depends on the indication and province. The 5 mg dose for BPH is listed on most provincial formularies, including Ontario's ODB and BC PharmaCare, typically with a general benefit or senior's benefit. The 1 mg dose for androgenetic alopecia is generally not covered as a publicly funded benefit in most provinces, since hair loss is classified as a cosmetic condition. Patients should check their specific provincial formulary or employer benefits plan, as private drug plans vary widely.

Can finasteride cause permanent sexual side effects?

During treatment, approximately 3–4% of men in clinical trials reported sexual side effects including decreased libido, erectile dysfunction, or reduced ejaculate volume, compared to roughly 2% on placebo. A smaller subset of men — the exact proportion is not established — have reported that these effects persisted after stopping the drug, a phenomenon sometimes called post-finasteride syndrome. Health Canada has updated finasteride's product monograph to require disclosure of this possibility, but the condition lacks a validated diagnostic criteria or proven treatment as of 2024.

How long does finasteride take to work for hair loss, and what happens if I stop?

Most men see measurable improvement in hair count at 12 months, though some notice stabilization of loss as early as 3–6 months. The drug must be taken continuously to maintain results — studies show that men who stop finasteride lose the hair they retained within approximately 6–12 months, returning to the trajectory they would have followed without treatment. There is no evidence that a finite course of finasteride produces lasting benefit after discontinuation.

Sources

All glossary termsUpdated 2026-05-22