A mood and sensory altering drug.
You could say something along the lines of:
"Hey, Friend, what's so good about weed? Why are you always smoking it?"
If he's smoking it for medical purposes, then just drop it, but if it's illegal and he's doing it to "look cool", then I would further ask questions about it.
Food and Drug Administration
Answer:
<em>A minimum of 48 hours' rest between circuit training is required for adequate recovery. You should perform one set of eight to 12 repetitions two times a week if you're just beginning. Increase to three days a week or to two sets, or both.</em>
Explanation:
