In a study conducted by Reilly et al., (1998) using 268 long term users of cannabis with regular usage of at least three times per week, the subjects gave reasons for their cannabis use as mainly for relaxation, having a feel good effect and to alleviate stressors in their day to day lives. They however reported feelings of anxiety or depression, lack of motivation, exhibition of paranoid ideation and some also reported respiratory symptoms. Beer (2007) explained that certain individuals with a Valine modification in the dopamine-regulating COMT (catechol-O-methyl transferase) gene are vulnerable to developing psychosis and cannabis can exacerbate psychosis in individuals with this defect in their genome. Experiments conducted by D'Souza et al (2004) described the existence of positive and negative symptoms of schizophrenia in the healthy people in their study who were given cannabis intravenously and also a transient acute psychotic episode in others. Early commencement of cannabis use on a frequent basis was noted as a strong predictor in the individual's future addiction to cannabis and an important relation to depression (Kalant, 2004). He further showed that there is evidence that memory and information processing in the children of women who are chronic users of cannabis were permanently affected and a susceptibility to other illicit drugs dependence in later life owing to early exposure.
Consider an example in which doing something is occupying your attention. Your attention might be occupied by driving down a narrow street without scraping the cars parked on each side; or by getting the cursor from the top left hand corner to the bottom right hand corner of your computer's screen; or by getting someone with whom your are in conversation to decide to take a certain course of action without pressurizing them. Your attention's being occupied in such actions cannot be identified with your attending to the events in the external world which they involve. In the example of driving down the narrow street, you could attend to exactly the same external movements and objects without being the driver at all. Similarly, in the example of moving the cursor, your pattern of attention to motions and symbols on the screen could be exactly the same as when someone else is operating the mouse which controls the cursor. Nor can the action's occupying your attention be identified with attention to some further external events or perceptual states. In the driving example, it does not consist in your attending to the movements of the steering wheel, or to sensations of pressure on the wheels and pedals. The experienced driver will not be attending to such things when his attention is occupied with the action of driving down the narrow street. Nor, again, is the object of your attention is any event of trying (whatever that might mean).