Ben Foster says drugs "definitely damaged" his body after he experimented with a performance-enhancing doping regimen modeled after disgraced athlete Lance Armstrong.

The actor revealed to BBC Newsbeat that to prepare for his role as Armstrong in "The Program" - a film based on the book "Seven Deadly Sins: My Pursuit of Lance Armstrong" - he took the drugs under medical supervision so that he could understand why athletes turned to the drugs to win competitions.

After experimenting on himself, it was easy to understand why athletes would risk their career and reputation for victory, despite the putting one's health in danger. "Go faster, go longer, go stronger," he explained. "That's why you take them. And they took drugs because they work. But they also can damage the body very long-term and in very serious ways."

Foster insisted that his use of the drugs was "legal" and its purpose was for a character study.

"I had a great doctor which helped me handle some of those consequences," Foster added. "But it took about half a year to get my levels right and I would say for any athlete, you have to ask, 'Where are your values?'"