LONDON VAUXHALL DEALERS

LaShawn Merritt could not have known when he bought penis enhancement pills over the counter from a local convenience store in Bradenton, Florida, that his embarrassment would go global. "It was more energy-wise," the American Olympic 400 metres champion says, suppressing a guilty smile when explaining his purchase of a product that contained the banned substance Dehydroepiandrosterone (DHEA) and which led to his suspension for 21 months.

"[There] was a condom and right beside it was [ExtenZe]. It was a 'boom boom', went-home-type deal. It was a poor judgment call from me. If I'd looked on the back and saw that the label [said] DHEA, I definitely wouldn't have taken it. I'd never think in a million years that I could buy something from a 7/11 and test positive for track and field."

Nor be asked to explain why he bought it in the first place. "Embarrassment was an initial reaction for a minute," he said, "but, when I thought about it, I'm pretty sure there's more than a couple of men here who've taken it. But I'm a pro athlete so I just forgot that part. When I was picking it up, I wasn't thinking about anything. It was just 'boom boom', to the house."

And now it's "boom boom" to the Olympics and Merritt is back in the big time. He is the first banned gold medallist to defend his title, a dubious distinction that does not sit well with Dai Greene, who says he will make his displeasure known if they meet in London. "If I'm in the relay team and we reach the final then there's every chance we'll be lining up against Merritt," the Welsh hurdler says. "I'll tell you now, I'll happily go and find him at the start and tell him to his face, 'You're a cheat and you shouldn't be here'."

Merritt is cool about that. "I have read [what Greene said] and I put it down and kept on about my business," he says. "I just looked at it as somebody else's opinion – it was, honestly, just nothing."

Was he interested in replying to Greene? "You know what, not really but, if we line up, we'll go at it like anyone else. If we get together in the four by four, I'm gonna do my job and he's going to do his job and USA are gonna bring the gold home. It is a little motivating but I've always been motivated without saying anything to anyone. This is what I love to do. If I didn't say a word all year I'd still be as confident."

You tend to believe him. Merritt has a quiet aura, one derived from natural talent and an admirable work ethic – although there are plenty of people in his sport who side with Greene. "There may be people here who think the same thing," he said at the US Olympic team media summit in Dallas. "People think what they think, but I have nothing to do with it. I have to continue to do what I do and that's work hard and show up."

He certainly showed up at the Prefontaine Classic in Eugene, Oregon, two weeks ago when he ran 44.91 seconds to beat a field that included the rising Grenadian Kirani James. The teenager, who beat Merritt on his return to international athletics at the world championships in Daegu last year in 44.60, false-started in the Prefontaine race but ran it anyway – and finished just a stride behind Merritt. Merritt also beat his fellow American Jeremy Wariner, the 2004 Olympic champion, as well as the twice Olympic 400m hurdling gold medallist Angelo Taylor and the Jamaican Chris Brown.

Wariner and Merritt will meet in the final US trials, starting on Friday. "He's a threat every time he steps on the track," Merritt says. "You respect your co-workers because you know how hard it is. But we're fighting for the same position."

It would, nonetheless, be a major shock if Merritt does not make it to London – although he wishes there was one other member of his family there to see him run. His older brother, Antwan, died in mysterious circumstances at college 13 years ago, and LaShawn to this day is not satisfied that justice has been done. "He never got the chance to see me run track," he says. "I'm here and able to do something and I have to maximise my potential. He was a musician who wanted to be an architect and he passed away at his first semester at college. He never even got a chance to start his dream.

"He went to Shaw University in North Carolina. Evidently he got into an altercation with a guy on a basketball court and the guy was part of this off-campus fraternity. That same night, the guy's frat brothers ended up coming to his dorm room, which was on the ninth floor, and he ended up out of the window. It was three big guys. He'd just turned 18 and was smaller than what I am now.

"He died a little bit later but the guys shouldn't even have got through security. There was a camera pointing right [at] the window but it wasn't working. Whoever thought that could happen? They were charged [with manslaughter] but there was some law which meant they couldn't prove that they [were responsible for his death]. One got a little bit of time and others got community service, so I don't think justice was served.

"It gave my life perspective. I learned when terrible things like that happen you just have to keep moving forward, because nothing else is going to stop. The more you sit there in your misery, it's not going to help. If I sit here and do nothing, then I'm only hurting myself. So I kept training. That's what I did during the drug stuff. I went back to school. I didn't finish my degree but I'm majoring in business management. I talked to a couple of local schools on how things in life may happen."

When Merritt failed his drugs test, he became a non-athlete. He always thought he would be reinstated but says it was tough to stay focused on a sport that had rejected him. "For two years I didn't get any money. With the help of some friends, I could pay my bills but not much more than that."

And, if his accountant had something to do with looking after his finances, it was his dead brother who provided the underlying motivation to return to athletics. "I think about my brother before every race because he never got the chance to see me run. He saw me play baseball, basketball and football when I was young but never at track. So I'm doing this for the both of us.

"Me and my brother were really close. He was five years older than me, and I was hanging with him and his friends some time. When I was a youngster he would tell all his friends that I was fast and I would race older guys in the street. He would come to all of my sports events and be the big brother, supporting me. He would give me money; he'd say if I hit two home runs, he'd give me 20 dollars, or whatever. He definitely played a big part when I was growing up.

"He was always a hard worker and I can remember him being in the house at high school, writing music for the whole band. He was a guy who had this talent for music. Even before I step on the track, I say a prayer which he's in and it just gives me strength. I know he's watching over me. I kiss my two fingers, I raise them as high as I can and then, after that, it's time to do what I was blessed to do. If he was here he would have loved to see me do it."

If Merritt does not keep his title, if James rediscovers that extra stride to beat him again – he maintains: "I really feel I beat myself in that race" – he might turn to American football as a second sporting career, having flirted with the option during his enforced exile, as a wide receiver. "It's still a possibility," he says. "It was serious in my mind. I was thinking I have to do something and I think I may still try out. I think am I going to regret it if I never tried it."

Americans love their goals and dreams. Merritt's fulfilment of his talent in Beijing four years ago has been tarnished but he is hanging on to it, regardless. And London, he says, will neither prove him guilty nor innocent.

"Gold wouldn't be redemption for me. I continue to train, to work hard, just as I've done ever since I was 18. If I win – when I do win – I won't think about what went on. It will just be a case of all the hard work I've done paying off. I don't feel I've got anything to prove. No pressure. I'll take it round for round. Now I'm here I'm just going to get the job done.

"I feel the drug testing itself was nothing. Something happened, I didn't read a label. To some people, it may be a cloud but, to me, I just made a mistake and I'm moving forward from it. I feel my case was unique."

Drug-taking in sport has long been an art and a science. It is wrong and it is widespread, but those who are good at it often profit. They risk their health and their credibility because they think it is a price worth paying, a delusion that is sadder even than their fall from grace. Merritt's is yet another case of an athlete claiming ignorance as a defence. It is pretty much the default position of anyone careless enough to get caught – and this one had the added piquancy of embarrassment.

"I was laying in bed, my agent told me, 'We got the letter and they're not letting you compete.' At first it was like when the police pull up behind you on the road and your heart just drops … oh, no. My agent thought it was funny … "

True. But how could an athlete be stupid enough to risk universal derision by using a product such as Merritt did in the pursuit of a possibly marginal advantage? Perhaps he is telling the truth, after all.