Thinning on top? What finasteride can and cannot do for you

Male pattern hair loss (androgenetic alopecia) affects roughly half of men by their fifties, and it often starts far earlier — a receding temple line or a thinning crown in the late twenties is completely typical. It is not a disease and it does not need treating. But if it bothers you, there are only two treatments with solid evidence behind them in Ireland: finasteride tablets and topical minoxidil. This guide is about the first one.

What finasteride actually does

Hair follicles on the top of the scalp are genetically sensitive to dihydrotestosterone (DHT), a potent by-product of testosterone. DHT gradually shrinks those follicles, so each growth cycle produces a finer, shorter, paler hair until the follicle stops producing a visible hair at all. Finasteride blocks the enzyme (5-alpha reductase type 2) that converts testosterone into DHT, cutting scalp DHT substantially. Less DHT means less miniaturisation.

What results actually look like

Be clear about the goal. Finasteride is far better at holding the ground you still have than at regrowing ground you have lost. Follicles that are miniaturised can thicken again; follicles that are gone and scarred over cannot come back.

Take standardised photographs at the start — same light, same angle, dry hair, crown and hairline. Memory is a terrible measuring instrument for something that changes this slowly, and photographs are the only fair way to judge at the six- and twelve-month reviews.

Side effects: the numbers, not the noise

Most men take finasteride without any side effects. A minority do not, and the sexual side effects in particular deserve a straight conversation before you start rather than a leaflet afterwards.

Two practical points. First, side effects are not something to endure quietly for the sake of hair — this is a cosmetic treatment for a benign condition, and stopping is always a reasonable choice. Second, if you develop any change in mood, do not wait for a scheduled review. Contact a doctor.

Who must not take it

• Women who are pregnant, may become pregnant, or are breastfeeding — finasteride can cause abnormalities of the external genitalia in a male foetus. Pregnant women should not even handle broken or crushed tablets. Coated whole tablets are safe to handle.
• Anyone under 18.
• Anyone with a known allergy to finasteride or any tablet ingredient.
• Men with a personal history of significant depression or suicidal ideation should approach it with real caution and only after an explicit discussion.
• Caution is needed in liver impairment, since finasteride is extensively metabolised by the liver.
• It is not licensed for female pattern hair loss in Ireland; different assessment and different options apply.

Interactions and things worth mentioning

Finasteride has few clinically important drug interactions, which is one reason it is a straightforward medicine to prescribe. What matters more is context: tell the prescriber about any prostate medication (including dutasteride or a 5-alpha reductase inhibitor taken for prostate enlargement — do not double up), any testosterone or anabolic steroid use, liver disease, planned fertility treatment, and any history of depression. Alcohol does not interact directly, but heavy drinking complicates both liver function and mood.

Fertility, planning a family, and the long game

Finasteride can reduce ejaculate volume and, in a small number of men, sperm parameters; these effects generally reverse after stopping. If you and a partner are actively trying to conceive and you are concerned, a break from treatment is a perfectly sensible option to discuss. Taking finasteride does not harm a pregnancy through the male partner — the teratogenic risk is from a pregnant woman absorbing the drug herself, not from semen.

First, rule out the causes that are not genetic

Not all thinning is pattern hair loss, and the ones that are not respond to entirely different treatment. A good consultation checks for these before reaching for a prescription:

• Telogen effluvium — diffuse shedding two to three months after illness, surgery, severe stress, crash dieting or COVID-19. It self-corrects.
• Iron deficiency, low ferritin, or vitamin D deficiency — worth a blood test, particularly with fatigue or heavy exercise.
• Thyroid disease — both over- and underactive thyroid cause hair loss.
• Alopecia areata — smooth, well-defined round bald patches rather than gradual thinning. A different condition with different treatment.
• Scalp disease — psoriasis, seborrhoeic dermatitis, fungal infection, or scarring alopecias where early specialist referral genuinely changes the outcome.
• Medicines — some antidepressants, retinoids, anticoagulants, beta blockers and chemotherapy agents cause hair loss.

The alternatives, briefly

How to get assessed at NOVAGP.IE

A consultation with an Irish-registered GP costs €39, seven days a week, with no evening, weekend or bank holiday surcharge. We take a history, screen for the non-genetic causes above, arrange bloods where they are indicated, and talk through the side effect profile honestly. If finasteride is appropriate and you want it, the prescription goes to your chosen pharmacy by Healthmail the same day. We review at three months and again at six to twelve, with your photographs side by side — and if it is not working for you, we say so and stop it.

Sources and further reading

• HPRA — search the Irish medicines register for finasteride product information
• EMA — 5-alpha reductase inhibitors safety information
• HSE — hair loss
• NICE CKS — androgenetic alopecia in men

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