McConaughey shed more than 40 pounds and pored over 16-plus hours of interview tapes, for example. At a recent installment of the Envelope Screening Series, the actor talked about his preparation and what his "secret weapon" was.
McConaughey's first resource was the cache of tapes that screenwriter Craig Borten recorded with Woodroof months before Woodroof's death in 1992.
"What I got from that was a lot of different variations for how to play the scenes," McConaughey said, adding, "That was very important. Also, not just the information that was there but how he spoke."
McConaughey then visited Woodroof's family members, who "opened up their house. They were very honest about who Ron was and who he wasn't. They did not try and glorify him and his martyrdom. They were really honest."
Perhaps most importantly, "They gave me what was my secret weapon, which was his diary. Which was the diary before he had HIV, and that's where I understood who the man was before this disease came on — which ironically gave him the first purpose and clear identity of something to fight for in his life. … He wanted to get out. I don't know where he wanted to go, but he was lost and wandering and was pretty lonely. And the ironic, sad thing is that this disease is actually what gave him something clear to fight and claw for 24-7."
For more from the cast and crew of "Dallas Buyers Club," watch the clip above and check back for daily updates.