Minoxidil and finasteride: how they work, results and side effects

Topical minoxidil is a solution or foam you apply to a dry scalp where hair is thinning. In the US and Puerto Rico it is sold over the counter in 2% and 5% strengths. Its FDA-approved label is to regrow hair on the top of the scalp, in men and women with hereditary pattern hair loss.

• Men: 5% foam, half a capful twice a day.
• Women: 5% foam, half a capful once a day.
• Using more, or more often, does not improve results, according to the label.

The label warns that it may be harmful during pregnancy or breastfeeding, and asks you to check with a doctor first if you have heart disease.

Patience matters. Per the FDA labels, men may see results at 2 months with twice-daily use, though some need at least 4 months; women at 3 months with once-daily use, and some need 6 months. The American Academy of Dermatology says full results usually take 6 to 12 months.

You may shed more at first. The American Academy of Dermatology describes a temporary increase in shedding during the first 2 to 8 weeks, which stops as new hair starts to grow. Do not quit because of it.

The most common side effects are scalp irritation, itching, dryness or flaking, and facial hair if the product runs onto your forehead or cheeks. Stop and see a doctor if you have chest pain, a rapid heartbeat, dizziness, swollen hands or feet, or sudden unexplained weight gain.

The American Academy of Dermatology warns that minoxidil can seriously poison cats and dogs, even a few drops: from licking your head or pillow, or chewing a tissue or the bottle. Store it out of reach, keep pets out of the room while you apply it, wash your hands well, keep pets off your pillow, and never put it on a pet. If a pet is exposed, call your veterinarian right away.

Minoxidil also comes as tablets, but the FDA approved them only for severe high blood pressure that does not respond to other medicines. The tablet label carries a boxed warning (the FDA's most serious): it can cause fluid around the heart (pericardial effusion) and worsen angina, and it usually needs a diuretic to prevent fluid retention. On that label, about 80% of patients grew more body hair.

For hair loss, much lower doses are used, and that use is off-label. A study of 1,404 patients in the *Journal of the American Academy of Dermatology* (2021) found the most common side effect was extra body or facial hair (15.1%), with lightheadedness (1.7%), fluid retention (1.3%) and a fast heartbeat (0.9%), and no life-threatening effects. A randomized trial in *JAMA Dermatology* (2024) compared 5 mg oral minoxidil daily with 5% topical minoxidil twice daily in 90 men over 24 weeks and did not find oral minoxidil superior.

Fluid retention can show up as ankle or leg swelling, sometimes with rapid weight gain; if it happens while you take oral minoxidil, tell the doctor, and if you are also short of breath, get emergency care.

That is why oral minoxidil needs a medical evaluation: your blood pressure, your heart, your other medicines and whether you could become pregnant. Never split someone else's blood pressure pills to use for your hair.

Finasteride 1 mg is a daily prescription pill. Its FDA label approves it for male pattern hair loss in men only, and it is not indicated for children. It works by lowering the hormone that shrinks follicles in hereditary balding.

• How long it takes: the label says daily use for 3 months or more is generally needed before you see a benefit.
• If you stop: the effect reverses within 12 months.
• PSA: finasteride lowers the PSA value (the prostate blood test) by about half. If you get that test, tell your doctor you take it.

The same medicine at 5 mg is used for an enlarged prostate; that is a different use and a different dose.

In the label's first-year studies, sexual side effects were uncommon but more frequent than with placebo: lower sex drive (1.8% vs 1.3%), erectile dysfunction (1.3% vs 0.7%) and ejaculation problems (1.2% vs 0.7%).

Since it went on the market, these have also been reported: sexual problems that continued after stopping, depression, suicidal thoughts, breast tenderness or enlargement, and male breast cancer. Tell the doctor about mood changes, a breast lump or nipple changes.

Pregnancy: people who are or may be pregnant should not handle crushed or broken finasteride tablets, because it can affect the genitals of a male baby.

MedlinePlus notes that men may take finasteride or dutasteride. Dutasteride works in a similar way, but the FDA has not approved it for hair loss: using it for hair is off-label and is decided in an evaluation.

For female pattern hair loss, the approved option is topical minoxidil, and spironolactone is used off-label; it must not be used in pregnancy. Read more in hair loss.

Many people search for minoxidil for the beard. The topical minoxidil label approves it for the scalp only, so using it on the face is off-label. Facial skin is thinner and irritates easily, and the product can run onto areas where you do not want hair. If you are losing patches of beard, that can be alopecia areata, and it is worth an evaluation before you buy products.