There has been a lot of discussion surrounding whether marijuana use contributes to or affects mental illness, particularly depression and anxiety. Most studies have shown that those who use marijuana, particularly beginning in adolescence, are more likely to suffer from depression and/or anxiety later on. Frequent use further raises this likelihood. Interestingly, those who suffer from depression and/or anxiety are not any more likely to use marijuana. Causality has not been definitively proven as to whether marijuana use causes depression and/or anxiety, but the relationship has been shown consistently.
Another related, possible consequence of marijuana use, especially for those who use marijuana often, is that it may damage the brain’s ability to process enjoyment. Studies have shown that people who use marijuana produce the same amount of dopamine (the brain chemical tied to pleasure and reward) as non-users, but that it does not create the same physical reaction for them that it does for non-users. And this lack of physical response indicates that marijuana users may have damaged the areas of their brains responsible for creating the feeling of enjoyment. Again, whether marijuana use causes the damage, or whether people use it to make up for existing damage, is unclear.