Yes weed can cause problems in people with mental disorders, like bipolar disorder for example. Weed, like many psychedelics, can amplify emotions that you are feeling. If you feel insecure, weed could make you feel more insecure. If you are depressed it could make you feel more depressed and so on. At the same time marijuana can, in a person of the right mindset, help. If you feel like smoking is causing problems, just give it a break for a little or cut back how much you smoke.