The film premiered on Saturday night, giving the moviegoing world its first glimpse of McConaughey's highly-anticipated performance as a Texas man diagnosed with HIV in the 1980s.
Based on the true story of Ron Woodroof, the film follows his frustration with the Food and Drug Administration and his enterprising smuggling of more promising drugs.
For the role, McConaughey lost nearly 23kg, and appears startlingly gaunt throughout the film.
After the film, though, McConaughey told the audience his weight loss wasn't the hard part.
"That was the easy decision," he said. "I would have been embarrassed standing here looking like I do now playing the guy."
Dallas Buyers Club will be released in the US on 1 November.
Watch the trailer here: