We always allowed out kids lots of freedom as they were growing up. The only unbreakable rule was to never drive after drinking or getting high. The kids could always call for a ride home with no punishment. Kids are going to experment with stuff, never think they won't.

Being open and forgiving about it kinda makes it less attractive I think. None of my kids got beyond trying drugs, but they do like to drink. I have daughters so I don't know if it is different with boys. Make sure they know that stoners often do not do well in school, if he already has big future plans, remind him of this.

If your child is high all the time, then I think a more firm approach is in order. But, if usage is recreational, I would not be too concerned.

That is all I can think of for now, accept being able to talk about stuff like that openly with your kids, you get to hear some funny stories from them that you would miss out on if such activities were not allowed. Kids that have to hide that stuff from parents tend to overdue it whenever they get the chance.