When balding men took the prescription-only drug finasteride, marketed under the name Proscar for the treatment of enlarged prostate glands, they found that their hair started growing back.
Now both the Food and Drug Administration in the US and the Medicines Control Agency in Britain are considering whether to grant a licence for a milder form of the drug to be used specifically to treat hair loss. A decision is likely to be taken in Britain early next year.
At present, Proscar is only licensed for prostate problems but Merck Sharp & Dohme, who make the drug, have been carrying out clinical trials.
More than 1,500 men took part in Phase III trials. After a year, a panel of dermatologists found 48 per cent of men treated with Propecia (a milder form of Proscar) had increases in hair growth compared with 7 per cent of men receiving a placebo.
Excessive hair loss stopped and there was regrowth of around 100 hairs in every inch of previously balding scalp. Self-assessment by the "patients" demonstrated significant increases in hair growth.
While almost all men experience a change in their hairline at puberty, around 25 per cent suffer "hairline retreat". The condition, which is hereditary, occurs when high levels of the male hormone testosterone are converted to a derivative, dihydrotestosterone (DHT).
High levels of DHT cause hair follicles to age prematurely and shrivel. Finasteride works by blocking an enzyme, 5-alpha-reductase, which converts testosterone to DHT.
Fred Morenberg, a 62-year-old divorcee, started taking Proscar for an enlarged-prostate condition three years ago. He said after eight months he noticed his hair was becoming "more robust" and now to the untrained eye it looks as if he has a full head of hair.
Mark O'Donnell, 31, told BBC's Face Value programme that losing his hair at the age of 22 was every man's worst nightmare "It's no fun being 26 and looking 36," he said. Over six years, he spent pounds 12,000 on different products. He learned about Proscar over the Internet and asked his GP to prescribe it for him. After two years, he says he looks as if he is just beginning to lose his hair at the front as opposed to being entirely bald. "I was a nasty person when I was bald ... I was bitter and felt cheated ... They will have to take [the drug] out of my cold dead hands."
Although, reported side effects of the drug include reduced libido, impotence and lesser ejaculatory volume, Merck Sharp & Dohme claim adverse reactions are "infrequent" - with just 1.8 per cent of patients experiencing decreased libido.
A spokesman for the Institute of Trichologists said last night: "We don't really know the long term side-effects until it has been used for a long time ... I'm not sure that some things are worth taking a chance over in life."
But John Mason, chairman of the institute said the drug was "relatively free" of side-effects and added: "As far as these men are concerned, impotence or the other side-effects doesn't seem to worry them compared to their hair."
He added that the effects were usually only seen in men with early balding patterns rather than those who lost their hair later in life.
Susan Aldridge author of Hair Loss - The Answers said that within five years she expected to see more specific drugs on the market: "The medical profession is taking hair loss more seriously," she said. "This is a step forward but it's not the answer."
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