Finasteride: prostate enlargement and male pattern hair loss

Finasteride treats benign prostate enlargement, easing symptoms such as difficulty passing urine, urgent or frequent urination and a feeling that the bladder has not emptied. At a lower strength it is also used for male pattern baldness, which the NHS says is prescribed privately rather than on the NHS.

It is a prescription-only tablet, sold as Proscar and Propecia among other names, and is generally not recommended for women or children. Only specialists prescribe it for women in rare cases.

Finasteride belongs to the 5-alpha reductase inhibitors. It prevents testosterone from converting into dihydrotestosterone (DHT). Less DHT means the prostate shrinks over time, and hair follicles on the scalp are exposed to less of the hormone that causes them to thin.

The effect is slow. For an enlarged prostate it can take up to 6 months to work fully, and for hair loss the NHS says improvement typically appears within 3 to 6 months. It controls symptoms rather than curing the underlying tendency, so stopping usually brings symptoms back.

The NHS gives 5 mg once a day for an enlarged prostate and 1 mg once a day for hair loss. Take it with or without food at about the same time each day. Swallow tablets whole with water and do not break or crush them.

Treatment is generally long-term, potentially several months or years. Stopping without medical advice risks symptoms returning.

• If under 6 hours have passed since the missed dose, take it; if more than 6 hours, skip it. Never double up.

• Finasteride is generally very safe in overdose, but call NHS 111 if you feel unwell after taking extra.

• An alarm or advice from a pharmacist can help with remembering.

Most men aged 18 and over can take finasteride. Tell your doctor or pharmacist if you have ever had an allergic reaction to it or other medicines, have had depression or thoughts of harming yourself, have severe bladder problems, or have liver problems.

More than 1 in 100 men notice erectile dysfunction, reduced sexual interest or ejaculation problems such as less or no semen. Speak to your doctor if they persist or worry you. The NHS notes that some men have had sexual side effects that continued even after stopping.

Rare effects, below 1 in 1,000, include chest lumps, pain, swelling or nipple discharge, which may be signs of a serious condition such as breast cancer; see a doctor or call NHS 111. Low mood or depression is another; the NHS advises stopping the medicine straight away if this occurs when taking it for hair loss. Call 999 or go to A&E for thoughts of self-harm. The NHS also suggests telling family or friends that you take it, since it may sometimes affect mood or behaviour.

A severe allergic reaction, with facial or throat swelling or trouble breathing, is a 999 emergency. Suspected side effects can be reported to the Yellow Card scheme.

Only very small amounts of finasteride are present in semen, so the risk to a pregnant partner is very unlikely. Manufacturers recommend condoms, although the NHS says experts generally agree this is unnecessary.

Some men have reported poor sperm quality or infertility, which is uncommon, and sperm typically returns to normal after stopping.

Finasteride is not affected by other medicines according to the NHS. The one named herbal interaction is St John's wort, which might stop it working as well. You can drink alcohol, drive, and eat normally.

Because finasteride lowers PSA readings, tell any doctor arranging a prostate cancer check that you take it. The NHS also suggests lifestyle steps for prostate symptoms: cutting down on fizzy drinks, caffeine and alcohol, avoiding nicotine, eating more fibre and emptying the bladder fully.