About half of all men will experience noticeable hair loss by age 50. It's the most common form of hair loss in men, it's caused by a well-understood biological mechanism, and it has effective treatments. It's also one of the most confusing areas in men's health — surrounded by oversimplified claims, legitimate concerns that get exaggerated, and a surprisingly wide gap between what the evidence actually shows and what men have heard.
This article covers the biology clearly, explains what finasteride does and how, and gives you an honest account of the side effect picture — not the worst-case forum version, not the dismissed-in-one-sentence version. The actual numbers, with context.
Why hair falls out: the mechanism
Male pattern hair loss — androgenetic alopecia — is driven by a hormone called dihydrotestosterone (DHT), which is made from testosterone by an enzyme called 5-alpha reductase. DHT binds to receptors in genetically susceptible hair follicles and gradually shortens their growth cycle. Think of each follicle as a garden bed: under DHT's influence, the growing season gets shorter and shorter each year until the plants it produces are so fine they're barely visible. Eventually, the follicle stops producing visible hair altogether.
The follicle isn't destroyed — it's suppressed. That's why treatments that reduce DHT can slow or halt the process, and in some men, partly reverse it. The genetic susceptibility is inherited, primarily through the maternal line (though paternal history also plays a role), and it determines which follicles are sensitive to DHT and which aren't. The sides and back of the scalp are DHT-insensitive — which is why transplanted hair from those areas doesn't fall out in the same way.
One common misconception worth clearing up: male pattern hair loss is not caused by excess testosterone. It's caused by sensitivity to a testosterone derivative, in follicles that are genetically predisposed to respond to it. Men with high testosterone don't necessarily lose more hair.
Hair follicles aren't destroyed by DHT — they're suppressed. That's why reducing DHT can halt the process, and for many men, produce visible regrowth.
What finasteride does
Finasteride works by blocking the enzyme (5-alpha reductase) that converts testosterone to DHT. At the 1mg dose used for hair loss, it reduces scalp DHT levels by around 60--70%. With less DHT available, the miniaturisation process slows — and often stops.
The evidence base is substantial. In clinical trials, finasteride stabilises hair loss in approximately 85--90% of men who take it, and produces visible regrowth in around 65% after two years of consistent use. Those are meaningful numbers. The effects are maintenance-dependent: stopping finasteride returns DHT to previous levels and hair loss typically resumes within 12 months, at its pre-treatment rate.
The timeline requires patience. Most men see stabilisation at three to six months, and regrowth — if it occurs — becomes apparent at six to twelve months. Men who stop because they haven't seen results at eight weeks haven't given the medication a fair trial. Hair follicles operate on cycles measured in months, not weeks.
The side effect question — with actual numbers
The most frequently raised concern about finasteride is sexual side effects: reduced libido, erectile dysfunction, and reduced ejaculate volume. These deserve an honest account rather than dismissal or catastrophising. Here's what the data shows.
In large randomised controlled trials, sexual side effects occur in approximately 3.8% of men taking 1mg finasteride — compared to 2.1% in men taking a placebo. That's a real difference, but a modest one. To put it in context: paracetamol causes liver enzyme elevation in about 2--5% of regular users; SSRIs (common antidepressants) cause sexual side effects in 30--40% of users. The finasteride numbers are real and worth knowing — but the scale is significantly smaller than the online conversation suggests.
Most men who experience these effects find they resolve on stopping the medication. Post-finasteride syndrome — persistent symptoms following discontinuation — has been reported and is the subject of ongoing research. The honest position is that it exists in a small number of men, is not well understood mechanistically, and is not reflected in trial data at the rates reported anecdotally. It's not nothing; it's also not a reason to refuse to engage with a medication that helps the large majority of men who take it without meaningful side effects.
Men with a personal history of depression may warrant more careful monitoring. Starting at a lower dose and assessing tolerability over the first three months is a reasonable approach.
Minoxidil: the other first-line option
Minoxidil — available as a topical solution or low-dose oral tablet — works through a different mechanism. It appears to extend the growth phase of hair follicles and increase blood flow to the follicle. It's effective in slowing hair loss and producing some regrowth in a proportion of men, though it works less predictably than finasteride and the mechanism is less well understood.
Many clinicians recommend combining both: finasteride addresses the hormonal driver, minoxidil supports follicle health through a separate pathway. The combination produces better outcomes in most studies than either medication alone. Oral minoxidil at low doses has become increasingly common as an alternative to topical for men who find the latter inconvenient.
Making the decision
Hair loss is benign medically — it has no health consequences beyond its psychological and cosmetic effects. Not treating it is a completely legitimate choice. For men who do want to treat it, finasteride is the most evidence-based option available, with a side effect profile that — when communicated accurately rather than through the lens of worst-case anecdote — is manageable for the large majority of men.
The decision should be made on accurate information. That's what this article is for.
If you're considering treatment for hair loss, a clinical consultation will give you a clear picture of your options, the realistic outcomes, and whether finasteride is appropriate for your situation.