what i have learned
as a pot user with over 29 years of experience using it, i think that pot does two things long term if used heavily:
One: it DEFINITELY can destroy self-confidence, both during and after the high. This is in people who have low self-esteem or low self-confidence to begin with. It basically takes what you have and magnifies it, either for good or bad. If you are the toast of the party, then you will REALLY be the toast. Or you could just be toasted. Or toast.
2: Ambition. This is the one major side effect I've seen from long term usage. It completely destroys your ambition IF YOU LET IT. Which is to say, if you have low or little ambition anyway (to get a job, keep working, being creative, practicing your instrument, painting, ect) then you will be knocked further down. This is usually the case with daily users. I found that when i restrict my usage to once a week OR LESS, I have lots of ambition and then I reward myself with a toke at the end of the week or whenever I feel I've accomplished a lot.
My two cents, which is worth so much less these days....