The actor, who lost three and a half stone for his role, said that it was tough on his family, before admitting that his wife wasn't attracted to him during that period.
Speaking to The Sun, McConaughey said: "The first time I saw myself on screen I thought I looked like a reptile.
"It was an initial shock but I was able to shake that for the movie. My family saw my weight loss day by day, so they didn't have that shock — but I look back and I think perhaps it wasn't the easiest on them."
McConaughey said that although his wife Camilla Alves was supportive, "perhaps it was not so appealing to be intimate when I was in that zone".
He added: "It was tough, but what I lost physically down below, I gained up top.
"I felt incredibly clear-headed and purposeful, and on set there were no starvation dramas. I just wanted to get on with the job and tell this incredible story."
The actor, who plays Ron Woodruff in the film, previously spoke about his diet and weight loss, explaining just how little he ate.
He said: "It was tough going, I'm not going to lie. The dieting was pretty hardcore. I was losing 7lbs every week. I'd have a Diet Coke, two egg whites in the morning, a piece of chicken, then another Diet Coke.
"That was rough. I got down to [143lbs] and I was always hungry, and irritable. My body resembled a little baby bird with its mouth open, crying, 'Feed me, feed me,' and you realise momma bird ain't going to feed you. It's hard."
Dallas Buyers Club hits UK cinemas on February 7.
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