'I tried everything - from herbs brewed with tiger's penis and jamu,' says the businessman, referring to Indonesian herbal remedies.

Nothing worked and his wife began to suspect he was fooling around.

Viagra, he says, saved his marriage. His doctor prescribed it as soon as it arrived here.

'It changed my life. I've become much closer to my wife. I use it twice a week,' says the father of two children in their 20s.

'You don't know the frustration a man feels when he is unable to perform sexually.'

In some cases, Viagra more than delivered a sexual fillip to marriages; it also brought the stork.

Prof Lim says at least three of his patients had children after they were prescribed the blue pill.

On the other hand, the sex drug has also been blamed for a litany of marital woes.

A 2005 New Zealand study involving women shows it can introduce unwelcome changes to sexual practices, tension and conflict in communication between partners, fears about men's infidelity and concerns about adverse health effects from use of the pill.

Prof Lim was recently berated by a 64-year-old patient's son for prescribing Viagra to his father. His mother had discovered the pills and suspected her husband was up to no good.

Meanwhile, private investigator Dennis Lee, 38, says he handles at least two marital-infidelity cases involving Viagra each month.

He once tailed a retired teacher whose newly resurrected sexual capabilities had led him to take up with a mistress from China.

The retiree told his family he was giving tuition lessons but, when these sessions became more frequent and longer, his children called in the PI.

Mr Lee says the man is still with his mistress.

Marriage counsellor David Kan, 42, says some wives blame Viagra for their husband's infidelities.

Mr Kan, who is also co-founder of The Family Life Centre, says: 'I won't say the drug itself causes infidelity, but the user will find it easier if he wants to stray.'

'If you blame Viagra, you can also blame mobile phones as they allow people to chat or exchange SMSes with their lovers in secret.'

Doctors point out that the drug is no miracle cure for all relationship, psychological or emotional problems men may have.

Business consultant Dicky Chua, 58, can attest to this. He tried Viagra several years ago, but all it gave him were headaches and nausea.

'I was going through a divorce and I had depression and self-esteem problems. Everyone thinks Viagra will turn you into Superman. Some men will learn the hard way it doesn't work for everyone,' says Mr Chua, who is now divorced.

He says his ED problems disappeared after he took care of his psychological and emotional issues.

Indeed, the perception that drugs like Viagra and Cialis can turn ageing Lotharios into sex machines has fuelled a whole cottage industry of imitations.

Drug manufacturers from India to China capitalise on Viagra's reputation, putting out pills and potions which claim the same, if not more powerful, effects - at a fraction of the price.

Doctors say that while genuine sildenafil drugs - which cost about $20 a pill - may cause side effects like headaches, blurred vision and backaches, they are not lethal if prescribed after thorough medical evaluation.

Prof Lim, who studies the effects of fake sex drugs, says: 'There are lots of conmen who go around saying their drugs are safe because they are made of herbs. Many men - especially the less well-off and less educated - will find the proposition very attractive indeed.'

In light of the Power 1 Walnut episode, the Health Sciences Authority has warned the public that any product sold on the street claiming to improve sexual performance should be considered dangerous.

Anyone caught selling these drugs can be jailed for up to two years and/or fined up to $10,000 for each offence.

Despite this, at Desker Road last week, one peddler was openly flogging sex drugs from every continent including Viagra, Cialis and Levitra pills at $5 a pop. He insists they are real and even offers a 'double refund' as guarantee.

'We not like pharmacy, sell so expensive,' he says in Singlish.

Prof Lim believes the controls lie in education.

'We have to start educating the public, especially the young, on the dangers of such drugs,' he says.

He adds that punitive measures should be targeted at purveyors of the trade.

'Targeting users won't work. They are driven only to satisfy themselves.'

Even if it means dicing with death.

This article was first published in The Straits Times on May 3, 2008.