Cillian Murphy doesn't want to smoke on screen again.

The 47-year-old actor frequently lit up in scenes as Tommy Shelby in 'Peaky Blinders' while his character in new biopic 'Oppenheimer', scientist J. Robert Oppenheimer - who died of cancer in 1967 - subsisted on little more than cigarettes and martinis, but he doesn't want to do it anymore.

He told The Guardian newspaper's Saturday magazine of Oppenheimer: “Cigarettes and pipes. He would alternate between the two. That’s what did for him in the end.

“I’ve smoked so many fake cigarettes for 'Peaky' and this. My next character will not be a smoker. They can’t be good for you. Even herbal cigarettes have health warnings now.”

Cillian pushed himself to lose weight for the role and though he wouldn't disclose how many pounds he shed, he admitted he ended up with an unhealthy outlook.

He said: “You become competitive with yourself a little bit which is not healthy. I don’t advise it."

The Irish star admitted the pace director Christopher Nolan worked made it easy to forget to eat or sleep and he was fuelled by "crazy energy".

He said: “It’s like you’re on this f****** train that’s just bombing. It’s bang, bang, bang, bang. You sleep for a few hours, get up, bang it again.

"I was running on crazy energy; I went over a threshold to where I was not worrying about food or anything. I was so in it, a state of hyper … hyper something. But it was good because the character was like that. He never ate.”

But Cillian insisted he didn't take a method acting approach to the role.

He said: “Method acting is a sort of … No,”

In 2007, Cillian played another physicist, Robert Capa in 'Sunshine', and he went to Cern, home of the Large Hadron Collider in Geneva, for research because he wanted to gauge scientists' opinions on a range of subjects including love, politics, and "infinity or whatever the f***".

He said: “I had dinner with all these geniuses. I’ll never understand quantum mechanics, but I was interested in what science does to their perspective.

"Because they have a completely different way of taking in information than we do.

"I remember one scientist saying, ‘I don’t believe in love. It’s a biological phenomenon, the exchange of hormones between the female and the male. That’s all. Love is a nonsense.’

"I couldn’t go along with that, obviously.”