Finasteride

To understand finasteride, you need one fact: the hormone that damages hair follicles isn't testosterone itself — it's DHT (dihydrotestosterone), a more potent derivative.

An enzyme called 5-alpha-reductase converts testosterone into DHT. In genetically susceptible follicles, DHT binds and progressively shrinks them, so each new hair grows finer and shorter until it's barely visible.

Finasteride blocks that enzyme. Less testosterone gets converted, so DHT levels fall — by roughly 60–70% in the blood. With less DHT around, follicles stop shrinking, and some recover.

This puts it in a different category from minoxidil. Minoxidil pushes follicles to grow despite the damage. Finasteride stops the damage at its source. That's why they're often used together — they're not redundant, they're complementary.

In women, the picture is murkier. Studies have produced mixed results, and the drug is used off-label. It works best in women with clear evidence of excess androgens. For most women, spironolactone is the more common and better-established choice — it blocks the androgen receptor rather than DHT production, and its safety profile in women is far better characterized.

Dutasteride is a related, more potent drug that blocks the enzyme more completely. It's used off-label for stubborn cases, and carries the same pregnancy warnings, more strictly.

1 mg daily is the standard hair loss dose. (The 5 mg tablet is for prostate enlargement; some people split it, though dosing accuracy suffers.)

With or without food. Same time each day.

In women, dosing varies and is decided case by case. Some dermatologists use higher doses in postmenopausal women. There's no settled standard, which itself tells you something about the state of the evidence.

Timeline: 3–6 months to see change; 12 months for a fair judgment. Slow.

Long-term. Like every hair loss treatment, benefits fade within 6–12 months of stopping. The DHT comes back, and so does the shrinking.

Handling warning — this matters even if you don't take it. Finasteride can be absorbed through the skin from broken or crushed tablets. Anyone who is pregnant or could become pregnant should not handle broken or crushed finasteride tablets at all. Intact, coated tablets are safe to touch. This is a real precaution, not a formality — it applies to partners and household members too.

Often combined with minoxidil. Finasteride stops the DHT damage; minoxidil drives regrowth. Together they outperform either one.

In men:

Reduced libido. Reported in roughly 1–2% in trials.

Erectile dysfunction. Around 1%.

Reduced semen volume.

Breast tenderness or enlargement.

These are uncommon, and in trials the rates were close to placebo — meaning many people reported them while taking a dummy pill too. Still, they are the effects that worry people most, and they deserve a straight answer rather than dismissal.

In women:

Menstrual irregularities

Breast tenderness

Headache

Reduced libido

Mood changes

Increased shedding in the first weeks, as with other hair treatments.

Birth defects. Finasteride blocks DHT, and DHT is required for normal development of male genitalia in a fetus. Exposure during pregnancy can cause serious malformations. This is the reason for every precaution around this drug — including not handling broken tablets.

Depression and suicidal thoughts. Reported, and now included in labeling in several countries. Take any mood change seriously and report it.

Persistent sexual side effects after stopping ("post-finasteride syndrome"). Some men report sexual dysfunction that continues after discontinuing the drug. Whether this is caused by finasteride remains genuinely contested in the medical literature — studies conflict, and no mechanism is established. It's a real source of concern for patients and it deserves an honest answer: the evidence is unsettled. Discuss it with your doctor rather than relying on internet forums, in either direction.

Male breast cancer. Rare cases reported. Report any breast lump, pain, or nipple discharge.

Allergic reaction. Swelling of the lips or face, rash, difficulty breathing.

It lowers PSA levels. This matters: finasteride roughly halves PSA, a blood marker used to screen for prostate cancer. If you have a PSA test, tell the doctor you take finasteride so they interpret the result correctly. Otherwise a concerning result could look normal.

Pregnancy: absolutely contraindicated. Finasteride causes serious birth defects in male fetuses by blocking the DHT needed for normal genital development.

This is why finasteride is generally reserved for postmenopausal women or women using rigorously reliable contraception. Any woman who could become pregnant and is considering it must understand this fully — and in most cases, spironolactone is the better and safer choice for female hair loss anyway.

Handling. Pregnant women should not handle crushed or broken tablets — the drug is absorbed through skin. Intact coated tablets are safe to touch. This applies to partners and anyone in the household.

Breastfeeding: contraindicated.

For men: finasteride is present in semen in tiny amounts. It is not considered a risk to a partner's pregnancy at these levels. Men do not need to stop finasteride when trying to conceive, though it can modestly reduce sperm counts in some — worth mentioning if you're having difficulty.

Do not take if:

• You are pregnant, could become pregnant, or are trying to conceive
• You are breastfeeding
• You are allergic to finasteride or dutasteride
• You have significant liver disease (discuss first)

Do not handle broken or crushed tablets if you are pregnant or could become pregnant.

Discuss carefully before starting if you:

• Have a history of depression or mood disorders
• Are due for PSA testing (finasteride halves PSA — your doctor must know)
• Have liver problems
• Are a woman who has not gone through menopause — in which case spironolactone is usually the more appropriate option

Not for use in children.

Can women take finasteride?
Some can, but it's off-label and it's mostly reserved for postmenopausal women. The evidence in women is mixed, and the pregnancy risk is severe. For most women with pattern hair loss, spironolactone is the better-established first choice — similar target, far better safety profile in women, and no birth-defect catastrophe risk if contraception fails.

Why is the pregnancy warning so serious?
Because DHT is required for normal male genital development in a fetus. Finasteride blocks DHT. Taking it during pregnancy can cause serious birth defects. This is also why you shouldn't handle broken or crushed tablets if you're pregnant — the drug absorbs through skin. Intact tablets are fine to touch.

How is it different from minoxidil?
Completely different mechanisms, which is why they're used together.

Finasteride blocks DHT — it stops the hormonal damage at its source.
Minoxidil improves blood flow and pushes follicles into the growth phase — it drives regrowth despite the damage.

One prevents; the other regrows. Together they outperform either alone.

How is it different from spironolactone?
Both are anti-androgens, but they act at different points. Finasteride reduces DHT production. Spironolactone blocks the androgen receptor, so DHT can't deliver its message. In women, spironolactone is more commonly used and better understood.

Will it cause sexual side effects?
In men, reported rates are around 1–2% — and in trials, the placebo rates were similar, meaning many people reported the same symptoms on a dummy pill. Most men have no issues. But the concern is real to those who experience it, and it shouldn't be brushed off.

Is "post-finasteride syndrome" real?
This is genuinely contested. Some men report sexual and mood symptoms persisting after stopping; studies conflict and no mechanism is established. The honest answer is that the medical community does not agree, and neither the alarmist nor the dismissive framing you'll find online is well supported. Discuss it with your doctor before starting, and take any symptoms you develop seriously.

How long until it works?
3–6 months to see change, 12 months to judge fairly. And it's long-term — stop, and DHT returns, and so does the thinning.

Does it affect prostate cancer screening?
Yes, importantly. Finasteride roughly halves your PSA level. If you have a PSA test, tell the doctor you take it, or a concerning result may be misread as normal.

What's dutasteride?
A stronger relative that blocks the enzyme more completely. Used off-label for stubborn hair loss. More potent, and the same pregnancy warnings apply — more strictly, since it stays in the body far longer.