ive been seein a psychiatrist and psychologist and theyve said that people who have very light symptoms of depression in their earlier stages when smoking marijuana it can actually bring the symptoms out more severely to the point of notice. marijuana is a depressant after all. It is also said to deplete serotonin levels in humans brains which has to do with motivation/happiness whatever... ever since i smoked weed this shit has occured juss feel hopeless, and it is very hard to reverse without prescription use...see a counselor