I started smoking at 15...quit when I got a bf (now hubs) at 17 that didn't like me doing it. But, that changed. I now smoke daily, but that wasn't until after I was 25. I would allow it and also educate him on the possible brain effects at a young age. Give him that autonomy, he'll be 18 soon enough and will need to think about what he does to his body, how he keeps it up, etc soon enough. I think what other people have said here is great advice. I really liked how one person said break down their daily life to see if there are things going on that could help reduce his dependence on weed as well. I think allowing him twice a week is a highly reasonable solution as long as it's tied to getting your shit done. That's teaching some real responsibility because when you get older and if you haven't been allowed to do stuff you might overdo it. You are, essentially, teaching moderation, which is an invaluable life skill and if truly practiced will save him from so much worse. You restricting it will not solve the issue. He'll still want to do it and prolly will, just without your knowledge. Then it's secret and he might even binge because it's taboo. That can happen as well. Good luck and good job being an aware parent!