It really depends. The biggest concerns over weed are memory loss, laziness, "gate way drug" and of course psychosis and death. Yes, you can be lazy and forgetful when high. That's just one of the side effects of the drugs in cannabis. Granted it can stay in your system for up to two weeks after use, but these levels are tiny compared to when high. Personally I do notice a big change in my energy and memory about a week after using, but I'm not aware of being deficient in that week. So long as you don't take it all day every day it's not going to ruin your life. It can even inspire people creatively, philosophically or scientifically both whilst high and after using, on top of its pain relieving properties. As for being a "gateway drug" it all depends on who you know and how you are. The theory being if you do weed, you'll come into contact with people who do harder drugs and get addicted. But that's entirely your choice. I get offered coke, mkat, speed and ecstasy all the time, but I say no. Now for the two big ones. Psychosis. The effect cannabis has on your system is from 6 different drugs. The one everyone knows about is THC. This gives you a shorter, more intense high and is also a psychotic. The other big contributor to a high is CBD. This gives a more mellow, longer lasting high. It's also a powerful antipsychotic. Most strains of cannabis have roughly equal amounts of the two drugs in them. The big exception being the UK. For reasons I don't know most plants grown in the UK have lower levels of CBD than elsewhere. Finally death. There's a really good article on Wikipedia [url=http://en.m.wikipedia.org/wiki/Effects_of_cannabis]here[/url] about the effects of cannabis. There's never been a single death from cannabis OD. It lowers your blood pressure, so if you smoke a lot it can exacerbate an existing condition, but otherwise it's safe.