Matt Damon has revealed that his only attempt at method acting, for the 1996 war drama Courage Under Fire, left him so unwell that he feared permanent damage to his health. Preparing for the small role of Andrew Ilario in October 1995, the then-relatively unknown actor devised an unsupervised extreme diet and exercise regime to appear gaunt, with no medical or professional oversight of the kind now standard on major studio productions. The experience illustrates how differently physical transformations for film roles were handled three decades ago, and why Damon has never repeated the approach since.

To lose weight rapidly, Damon ran 13 miles a day while eating almost nothing but chicken breast, a self-devised plan he later admitted "could have killed" him. He said he felt genuinely ill during and after filming, telling no one for fear of confirming how serious it was, and it took a prolonged recovery period, including medication, after a doctor warned his heart may have been permanently affected. Reflecting on the episode, Damon said he "went too far" and would never attempt method acting again, calling it more harmful than beneficial.