I don’t want to talk about the names of the drugs I took. Even discussing it feels tricky because it isn’t something I’d recommend to fellow actors. These are very serious chemicals and they affect your body in real ways. For my own investigation it was important for me privately to understand it. And they work.

Foster went on to say he “lost his fucking marbles” while filming THE PROGRAM.

'There’s a fallout. Doping affects your mind. It doesn’t make you feel high. There are behaviors when you’ve got those chemicals running through your body that serve you on the bike but which, when you’re not …' He shakes his head. 'I’ve only just recovered physically. I’m only now getting my levels back.'

When asked how the "fallout" manifested, Foster said “I don’t know how to separate the chemical influence from the psychological attachment I had to the character. If it’s working, it keeps you up at night. This is losing your marbles, right? They’re definitely rolling around. They’re under the couch but they’re retrievable.”

The actor also talked a little about the Armstrong doping scandal:

On one hand, he’s a lying doper who tricked the world. On the other, he’s a young man who faced cancer. It changes you. And when you go to war it changes you. That’s what Lance did – he went to war with his body. That shifts your consciousness. He started training within a culture that was doping: you’d have to go down 18 riders to find a clean one. He survives death, the story catches fire and he recognizes that. He’s a smart man. He says, ‘I can do some good with this.’ He raised half a billion for cancer research. We just don’t like him because he was Jesus Christ on a bicycle. We’re mad he came back from the dead, saved the sick and then turned out to be full of shit. And we’re punishing him because he didn’t apologize in the way we’d like. Americans love a good apology. He wouldn’t do that.

Foster on playing Armstrong:

The word I’m leaning toward is ‘infected’. I tried to infect myself with him. Get him into my system...It was important to get his gait, his riding style. I talked to people who had the aerodynamics of his body on a computer system so I could get the hump in the back, the heels slightly out. It’s almost a duck pedal. It’s not a delicate ride. It’s violent, which is also why he’s such an exciting rider. It’s like he wants to break the bike.