There was an article not long ago about a person in china who overdid it with the ‘cupping’ and ended up with horrible disfigurement. The procedure breaks cappilaries in the skin and can cause necrosis.
It’s worked for me! I have a kit to do it to myself, although it’s less effective then having a pro do it.
I watched a video of Michael Phelps having it done. I think he had 4 or 5 cups on his left shoulder blade and his back. It was really weird looking.