After breaking up with his long-term partner, John Browne worried that returning to the dating scene would not be easy. But as the 36- year-old chef sat down for dinner with a young woman, he knew what he was feeling could not be dismissed as nerves.
His heart was beating too fast, his head was thumping and he was drenched in sweat. The British father-of-two felt so ill that he feared he was having a cardiac arrest.
Worse, John thought the fact that he was feeling so wretched could be his own fault. Anticipating how the night might unfold, before leaving his home he'd swallowed a small, blue, diamond-shaped pill.
He'd purchased the drug online, paying £25 for what the website claimed were ten Viagra pills. But far from having the desired effect, the pill had left him horribly ill. "Before I even got to the date, I started to feel really hot and sweaty," he said. "I thought it might be nerves - but then my heart started going really fast, I got a headache and felt a bit woozy."
Unsurprisingly, the date did not go well, and by the time Mr Browne got home he was feeling so ill he considered heading to A&E. In the end, he just collapsed in bed.
"I felt horrible for two days," he said. "I couldn't sleep, my nose was blocked, I was dehydrated and I had red blotches all over my face." A quick internet search of what a real Viagra pill should look like confirmed that the ones he had purchased were fake.
"I crushed them up and flushed them all down the toilet, because there was no way I was going to take them again," he said.
"I only took them as a back-up. I'd never had any problems before, but I just wanted to be sure. I would never buy anything like that online again, and I wouldn't recommend anyone else to do so either."
And there are plenty of people who should take heed of his warning.
The increased availability of such drugs via the internet makes getting hold of them much easier. Men like buying them online, rather than through their GP, because it spares their blushes.
A growing demand
There is also undoubtedly a growing demand. As well as those who have a medical condition for which Viagra or similar might be correctly prescribed, younger men are using them for sexual enhancement or are even taking them with other recreational drugs.
Fake Viagra can be bought for as little as £1. Other similar pills are illegal, unlicensed generic erectile drugs from India, where they have been made in labs that would not meet British safety standards.
Analysis of these pills has found them to contain everything from gypsum (which is also used to make plaster of Paris) to printer ink, brick dust and even highly poisonous arsenic.
They are often manufactured by criminal gangs who have moved into the market in response to increased demand.
This demand is largely driven not by the elderly and infirm, but by many younger men who feel under pressure to perform - whatever the risks.
"Unlicensed medicines can be dangerous, as they may contain incorrect ingredients and impurities," warns Alastair Jeffrey, head of enforcement at the Medicines And Healthcare Products Regulatory Agency (MHRA). "There is no way of knowing if they are manufactured to acceptable standards of quality and safety. Those involved in the illegal supply of medical products aren't interested in your health - they are only interested in your money."
Indeed, just how big the potential profits are was highlighted by the recent successful prosecution of a gang that was raking in up to £60,000 a week selling fake Viagra across Britain and beyond.
Users not surprising
Dating expert Hayley Quinn said that in her experience the use of Viagra-type substances among young professionals is not regarded as being out of the ordinary.
"Either people are seeking to have a heightened or longer sexual experience, or perhaps they're taking them to offset the effects of other drugs and alcohol," she said.
"For men, particularly, I think there is a lot of pressure on performing, so when they have a new partner there will be a lot of anxiety. Even if the men do not actually need it, I think having something like that will often be seen as a crutch."
That is very much the experience of 33-year-old Peter Jackson, who has been regularly using erectile dysfunction tablets for the past two years.
He purchases pills online from a company based in India. The pills are sold as Viagra and each one costs £1.
"I started taking the pills after my marriage broke up," said the engineer. "We were married for nine years and I thought we were happy, but my wife walked out on me, taking the two children.
"We had a normal, healthy sex life and I didn't have any performance anxiety. Once I was single I started dating online, and I've discovered it is a whole new world out there.
"I'm attracted to younger women in their 20s, but they have a much higher expectation of performance than my wife ever had.
Is online porn to blame?
"Maybe it's because they have more access to online porn, but they expect you to be far more active and inventive, and to be able to make love two or three times a night.
"I work full-time and I just don't have the energy. I had one totally disastrous date when I couldn't perform, and the shame was intense. I had to pull my trousers on and slink home."
He adds: "I wouldn't be prescribed Viagra because I don't have serious erectile dysfunction or a medical need - I'm a normal healthy young man in every other way.
"But the first time I took one of these pills, the effect was instantaneous. I felt on top of the world - as if I could go all night."
There were, however, deeply unpleasant side-effects - everything from severe headaches to fainting fits and dangerously high blood pressure.
"I once collapsed after taking two pills in two days, and I was in a state of severe dehydration," he says. "I didn't see a doctor, though, because I was too embarrassed. I just put myself to bed and waited to get better.
"I know I shouldn't still be taking the pills but I feel under such pressure to perform in bed that I have developed a dependence on them. I don't think I could get an erection without them, and they mean I can perform for much longer. But goodness knows what they are doing to me."
It's not for everyone
Indeed, the reason that Viagra is a prescription medicine is because it is not suitable for everyone and should only be taken with guidance from a medical professional.
Not only can it affect how other drugs work, but before prescribing it a doctor would want to know about any pre-existing medical conditions, such as kidney problems, low blood pressure, a heart attack or stroke.
But with fake pills, there is the added danger that it is impossible to know what the pill contains - whether that be the amount of active ingredient or the other fillers it will have been bulked out with.
It is also impossible to know in what type of conditions they were manufactured.
It is for all these reasons that experts warn against buying the drugs online - advice that 31- year-old Leo Darwin has studiously ignored, despite suffering deeply unpleasant side-effects. He buys the pills for as little as £1 a go from a friend, who in turn orders them from abroad on the internet.
"I've been using fake Viagra pills for a couple of years and I've had quite a few health scares with them," said the events manager.
"After being given one packet by a friend, I had a fainting fit. My blood pressure soared and I was drenched with sweat. My vision also went blurry, and I could see things in a strange colour. I also get raging headaches.
"I never should have started taking them, but the thing is that women these days seem to expect a star performance.
"When I take fake Viagra, I can last about an hour.
"Maybe it's the proliferation of online porn, but a quickie these days just does not seem to count.
"Sure, the side effects can be very worrying, but I'd still rather suffer that than the indignity of not being able to perform as well."
A deeply worrying statement - but, no doubt, one that will be music to the ears of the unscrupulous gangs making a killing cashing in on society's latest insecurity.