In the latest research on chronic marijuana use released by American Psychology Association, they found no evidence suggesting impact on physical or mental health for the subjects in this over 10 year longitudinal study.
The research was conducted jointly by Pittsburgh Medical Centre and Rutgers University to look at 408 males’ differences in physical and mental conditions from 15 to 26 to their mid thirties. The subjects were separated into 4 groups of different levels of marijuana usage and found no significant differences in any of the groups.
This is one of the first few studies to look at marijuana use in a long term perspective and it has a promising start for many future researches.
You can find the full report here