McConaughey: I became a hermit
The 44-year-old, who is up for an Oscar for his performance as HIV-positive rodeo-riding electrician Ron Woodroof, admitted he shunned contact with people so he could focus on preparing for the role.
"I basically became a hermit and surrounded myself with everything Ron Woodroof," he said.
"All my social engagements - didn't have those, didn't go out for dinner, couldn't go out in the sunshine. I basically stayed in and studied everything Dallas Buyers and Ron Woodroof and enjoyed, really, every minute of it."
Matthew also lost 47lbs for his character, as the disease ravages his body.
"It was hard but as an actor to have something that you can give your full singular focus and commitment to on as many levels as possible was wonderful," he said.
"To be able to, for six months of my life, really focus on doing everything I need to do to best tell the truth on Ron Woodroof was a pleasure. And I never got complacent so that physical transformation and weight loss really structured my life that helped me commit to what I need to do."
The actor, who has already won Screen Actors Guild and Golden Globe prizes for his performance, credits his wife, Brazilian model and designer Camila Alves - with whom he has three children under six - for helping him through the process.
"I'm very fortunate. I have a highly supportive wife and family and when Dad goes to work, they help me do whatever I need to do and insulate me in a way that I can get the work done," he said.
Dallas Buyers Club, also starring Jared Leto, opens in cinemas on February 7.