Well, right and wrong gets into a much more in depth argument as to whether there even is such a thing...but I digress. Assuming there is a "wrong", no...I don't think smoking weed is wrong. You should be able to do what you want in your own time as long as it doesn't hurt anyone other than yourself. To me, ODing on hydrocodine isn't wrong assuming you have no friends or family ties, hence not hurting anyone indirectly.
This being said, weed (as with alcohol and other drugs) is best in moderation. When it starts to affect your life in a negative way, it is a problem...if only to you. And, from personal experience, grades and general productivity go way down when you are high. It doesn't take a rocket scientist to guess that if you are high all the time, you're not getting anything done.
Moral...it's not wrong and if it makes you happy, then go for it. But be warned, your grades aren't going to go up and there's always the risk of the law finding out and coming down harder than is necessary.