The Oscar-winning actress had to have the injections as her full pout was causing problems for the lighting technicians on set.
Hudson told chatshow host Oprah Winfrey that she reluctantly had some surgery on her upper lip to alter her deep Cupid's bow.
Speaking on Oprah's Next Chapter, which will air today (September 9) in the US, she said: "When I did Dreamgirls I actually had to get my dent right here injected because it was affecting the lighting.
"And when I got it done the doctor was like, 'I do not want to do this. Do you realise people come in here and pay to have the lips you have naturally?' And I was like, 'I don't want to but I have to for the movie!'"
Hudson won an Oscar for 'Best Supporting Actress' in 2007 for her role in the film.