Make him aware that he has to be careful where he buys it from as some dealers can mix bad stuff in with it. It’s just weed, so not a big deal in comparison to what his friends might be taking, but yes he is still young. If it were me I’d tell him he is free to experiment safely once he is eighteen but until then it’s a no no.
My husband would probably get our son to smoke it with him and give him a proper talk about safety as he is more worldly than me.
I’d not be over the moon either, but it’s definitely not the worst thing he could take. I’d ask him if he’s aware how expensive his habit gets over time? Whose money is he using to buy it? If he has not got a job you could remove his allowance as a a punishment, and that seems like a good punishment to me without getting too OTT. After all, you don’t give out pocket money for it to go on smoking...
Can I just say I like that you aren’t being all crazy over this with him immediately. I know I would struggle not to. But I also know it would make things worse. With drugs the best thing you can do in my opinion is to make sure your child is informed (not just lectured at tho) and accept they will do what they want to do in the end.
Btw, I would also approach this subtly, so see what reaction he is expecting. Is he raring himself up for a confrontation, or is he already scared of what you would say and expecting a huge fight if he is discovered? If he is a typical angry rebellious teen, I’d say better to tread softly or you’ll drive him further into it in his rebellion.