I"ve heard that weed changes the way your brain releases dopamine. From personal experience, low dopamine levels can definitely cause depression. To counter this you could take an L-Tyrosine supplement, which is a precursor to dopamine.

Image:Tyrosine metabolism.png - Wikipedia, the free encyclopedia

I have mild ADD and am on Vyvanse (l-amphetamines, like Adderall); I noticed that it seemed to deplete the dopamine in my brain and I would crash in the evenings. I took L-Tyrosine and the problem went away.
Sweet_Leaf_91 Reviewed by Sweet_Leaf_91 on . Smoking all week and feeling depressed I've been smoking all of last week, all day, everyday. And now as I've totally stopped for a break, I've gotten many of the symptoms of clinical depression. Does anyone have any advice or anything? It'd really mean a lot, thanks. Rating: 5