It’s not recent, maybe it was made before 2000.
The protagonist is a young boy (a teenager?).
He has an uncle called Leon or Lionel or something similar.
His uncle spoils him and the boy’s mother thinks that he’s a bad influence on her son, so she’s trying to stop him from spending time with Leon.
The boy’s mom is missing a big chunk of her buttocks from an old accident when her brother sicked wolves or dogs on her.
As for the movie in the theaters, all the boy’s friends go to see it except the boy and they all go crazy.
The cashier at the movie theater tells the boy how could he make them normal again, but I don’t know what it was.

Answered question

what country was this from? was it a horror or a kids movie?

It’s probably from the US and I don’t think it was a horror but it wasn’t a kids movie either.

the hardest part of this is the movie makes them crazy, and that is already a search word for any film. i am having trouble thinking of the exact way someone would have written “movie makes people crazy” in a review to search it. i haven’t found the exact combo of words yet, any suggestions? for some reason i feel like this was a tv episode of one of those serial shows like friday 13th, goosebumps, etc. You said you don’t think it is kid based though….maybe a mystery or adventure genre? sci fi?

“i haven’t found the exact combo of words yet, any suggestions?”

If I knew the right combo I would search for it myself. 🙂
There are many ways to put it, it could be a curse, being possessed, being hypnotized, mind controlled, I still give it a try now and then.

I said that it’s not a kid movie because in the original question it’s labeled as a 16+ movie but it’s not a horror. So probably an adventure movie or a mystery, thriller…