It was the ultimate serendipitous discovery: a failed heart medication that became a multibillion-dollar erectile dysfunction drug. But the blockbuster story of Viagra could have ended differently were it not for the frankness of the Welsh miners who took part in a clinical trial just before the drug was due to be scrapped, according to Viagra’s co-inventor. Speaking before the screening of Men Up, a new BBC drama, executive produced by Russell T Davies, about the ordinary middle-aged Welsh men who took part in early trials, Dr David Brown said the drug’s unexpected side-effect was almost overlooked. “The whole thing could’ve been totally missed,” said Brown, a former medicinal chemist at Pfizer. “I don’t think there would be a drug around if that one miner hadn’t put his hand up.” Brown was leading the development of the compound sildenafil as a potential angina treatment but its prospects were not looking promising, and by 1993 Pfizer had all but decided to abandon the programme. “They basically said, ‘You’ve wasted money for eight years. We’re going to close it down.’” said Brown, who now runs a company, Healx, that uses artificial intelligence for drug discovery. As a last roll of the dice, a study was run at a clinic in Merthyr Tydfil, south Wales. “We weren’t sure we’d got the dose quite right,” said Brown. “We thought maybe if we increased the dose we’d get a bigger effect in angina.” The town, which had been plunged into poverty and unemployment after coalmine closures, had plenty of willing volunteers. As Brown recalls, the men were paid £300 to participate in a trial of the drug, which involved staying in the clinic overnight, having blood samples taken and being monitored. “In the morning, the young lady who ran the study gave them a questionnaire,” Brown said. “There was always an open question at the end asking if there were any other effects that you noticed.” Some may have been inclined not to broach the subject, but one man raised his hand and shared that he “seemed to have been having erections all night”, according to Brown, who added: “He must’ve been on the highest dose.” Other volunteers chimed in with similar experiences. Pfizer’s clinical associate reported the unusual side-effect to Brown. “She was quite an attractive young blonde lady. She blushed terribly when she told me this,” he said. “I said, ‘I think I understand why this is happening.’” After further investigation, it turned out that the drug, designed to relax blood vessels around the heart to improve blood flow, was having the same effect on arteries within the penis. Brown and a medical colleague immediately saw the commercial potential, but his boss initially rejected the idea of pivoting to an impotence treatment. “It was one of those pivotal moments in my mind,” said Brown. “I went and closed his office door and said, ‘I’m not leaving this room until you give me the money’. I could’ve lost my job, but an hour later he gave me the money.” Brown said it was “disconcerting” when reviewing paperwork of previous trials to discover that erections had been reported several times by other volunteers, but that this information had not been relayed back – presumably deemed inappropriate or irrelevant. “It could’ve been missed if that one miner and our clinical research associate had not said something,” he said. “The drug wouldn’t exist.” Viagra has spawned endless material for comedians, but for Brown and colleagues, impotence represented a huge unmet medical need rather than a subject for sniggering about. “Pfizer are incredibly commercially minded,” said Brown. “When they see big bucks they’ll go for it fast. As soon as the people in New York were told they immediately got it. The drug went from dead to number one in the global portfolio in two weeks.” The drug was launched commercially in 1998, becoming one of the most-prescribed drugs in history and improving millions of people’s lives. Despite his role in the discovery of Viagra, Brown says men do not tend to thank him for the invention – or even raise the subject of erectile dysfunction. “I’ve never heard any man mention it to me,” he said. “It says a lot. There’s still embarrassment about sex and men having impotence. There’s still a huge taboo.” He has some misgivings about the Viagra trials providing inspiration for Men Up, which will air over the Christmas period – but says he will be watching the show. “It worries me a little bit,” he said. “I’m a rational scientist and the history of the invention is important for the philosophy of science. Breakthroughs are rare and understanding what leads to breakthroughs is important in science. When it comes to drama for television I can imagine some of the facts will be a little bit different. I’d prefer it was factual.”