Hi!
The answer is your tongue
Maintain a weight below the normal range.
It strengthens your bones to be able to handle large amounts of pressure and weight on your body. I know this isn't related, but when a person breaks their ankle or something else they tend to heal quicker because they're athletes. So one way or another, increasing strength, helps to increase your capacity for exercising.
Yes it is because many drug users use things such as syringes and needles and thats how it is spread and also they have very low immune systems most of them making it a higher risk of them to get a infectious disease such as HIV,Aids