Not taking good care of themselves. Not being active, poor hygiene, bad diet, weak immune system etc
The glycemic index predicts the way certain foods affect blood sugar levels.
There are obviously A LOT of them. Like how your brain is slowly deteriorating, which is scary and dangerous. I can't cover everything but I have a website link you could visit that talks about this subject
https://www.drugabuse.gov/publications/research-reports/heroin/what-are-long-term-effects-heroin-use
