it affects different people in different ways
It seems to make people think they are awesome...unless you are one of those people who gets paranoid...and in that cause I imagine the effect would be negative because anybody who would give them self a bad trip on a regular basis must have a substantial amount of self loathing.
...only if you eat too much!
Indirectly perhaps? There isn't like a weed/self esteem correlation.
Obviously if you're asking.