If you're younger than 18-ish, I'd be judicious in my cannabis use. Why? Because there have been few, if any, studies done on the longterm effects of heavy cannabis use on a developing (e.g. young) brain. There might very well be some pretty harmful consequences. I don't *think* there is, but since there's no evidence either way, hey, it's your brain, it's YOU, and I'm not sure that getting high at that age is worth the risk.

On the other hand, I started smoking at 15, although not heavily until 18, and I came out more or less okay. This is why I suspect there may be no problems even for a young, developing brain. But still, there *could* be problems associated with heavy cannabis use on a developing brain, and I just happened to dodge that particular bullet. Who knows. You weigh the risks and make your own call; I'm just pointing out that it's not necessarily a totally frivolous decision. But I don't have to live with the consequences of your decisions -- you do.