HE RECALLED how wives used to drag their husbands in to see him for their problems in keeping erections up.

Professor Peter Lim, 58, a urologist in private practice at Gleneagles Hospital, said that back in the 1980s, he would get calls from women making appointments for their husbands two to three times a month.

When the couple walked into his office, the wife would usually declare: "Doctor, help him, he can't get it up!" The men would usually sit there, mortified.

Those awkward moments all disappeared with the introduction of a little blue pill - Viagra. Nowadays, "men walk into the clinic and declare they have erectile dysfunction", he said.

Viagra, which turned 10 years old yesterday, has been prescribed to about 35 million men in 120 countries across the globe. Since its launch in 1998, about 1.8 billion pills have been sold, said Pfizer, the company behind the drug.

The pill works on muscles in the penis which control blood flow. It allows more blood to circulate into the penis when there is sexual stimulation, thus causing the erection.

Erectile dysfunction is usually linked to ageing and related conditions such as high blood pressure, but about half of all his patients are younger than 50 years old, said Gleneagles Medical Centre's senior consultant urologist Ho Siew Hong.

More men are also coming forward for help with their sexual health because there is now an effective, yet painless way out.

Before Viagra was introduced, patients had to make injections into the penis, use a penis vacuum pump and a rubber band to engorge the penis, or "non-specific medication" such as plant extract supplements, Dr Ho said.

"Injections worked, but there weren't any non-uncomfortable alternatives," he said.

Many patients thus went without sex for months, even years.

One patient, who only wanted to be known as Mr Tan, 53, went celibate for almost five years, before he discovered "the wonder drug that changed the quality of my life".

He tried hormone treatment, traditional Chinese medicine, even acupuncture, spending a few thousand dollars. Nothing worked.

He became frustrated and depressed because he could not have sex with his wife. At one point, before he told his wife about his problem, she even suspected "I was having a fling outside because I avoided having sex with her".

The first time he tried Viagra, "I couldn't explain how I felt".

He declared: "It was simply fantastic."