I remember watching a movie in the mid-2000’s, it could of been a 90’s movie though, no clue.
It was a old style anime movie, where a boy’s dad gets killed by arrows, and his dad hides him in a cave. The boy travels into the cave a bit and eats a weird plant, gets in trouble with something because of it. Then the other part I remember is he has to somehow find this herb again.
Gandahar (Light Years) (1988)
Sorry! Wrong Laloux! This was Les Mâitres du temps (Time Masters) (1982).