The movie started out pretty good, Demi's character, Elizabeth Sparkle, was a video fitness star and a narcissist (IMO). Her manager fired her when she turned 50. She found out about The Substance and started using it. What transpired after that also started out good, although a bit weird.
Elizabeth wasn't reaping the benefits from The Substance and Margaret Qualley's character, Sue, just started taking and taking. This is where it went downhill for me, especially when Sue pulled a chicken leg out of her navel.
This was supposed to be a horror/sci-fi film, but I found myself laughing during the last hour of the movie. By the end of the movie, it was just downright hysterically funny.
Based on the other reviews, I seem to be almost alone in my review. Oh well. The moral of this story is be careful what you wish for and don't be so vain.