The Program: Chris O'Dowd says Ben Foster was 'smart' to take drugs for Lance Armstrong part

Foster plays the disgraced Tour de France cyclist in Stephen Frears' biopic

Ben Foster plays Lance Armstrong in Stephen Frears' The Program

Chris O'Dowd has praised co-star Ben Foster's "really smart" decision to follow disgraced cyclist Lance Armstrong's doping programme for his lead role in The Program.

Foster revealed last week that he had taken drugs to help him understand the challenging part and O'Dowd, who plays investigative journalist David Walsh, reckons the research idea "makes sense".

"With something like that you know it's not going to harm you necessarily and you're going to have to perform so much [while filming]," he told the BBC, adding that it is difficult to portray drug use if you have never tried the substance yourself.

"I think if you have to take drugs in a role, it's very hard to do without taking the drug at some stage in your life," he said. "I'm not advocating that you [should], but I'm sure it probably wouldn't hurt your performance.

"It might hurt you as a human being but it would be silly to say that would not be a good way in to knowing [what it feels like]. That's not to say you should or you shouldn't, but you can understand the validity of it."

Performance enhancing drugs are illegal in sport but can otherwise be prescribed to patients in medical need. Foster experimented with "condensed" doping under a doctor's supervision, and also trained by cycling the Tour de France route with professionals.

He did not tell The Program's cast and crew that he was taking drugs but when director Stephen Frears found out, he simply said "he's still alive".

"It happened, there's nothing I can do about it, I can't turn the clock back," he told reporters at the Toronto International Film Festival. "The truth is, he's so good in the film and I'm so grateful to him for being that good.

"I'm not interested in the process by which people arrive at their performances, I just expect them to turn up on the first day and be brilliant."

Ben Foster playing Lance Armstrong in The Program (Larry Horricks)

Foster made his confession to the Guardian but insisted that it would not recommend undergoing drugs programmes to fellow actors. "These are very serious chemicals and they affect your body in real ways," he said.

"For my own investigation it was important for me to privately understand it. I tried to infect myself with him, get him into my system. I've only just recovered physically."

The Program reaches UK cinemas on 16 October.