Some people have underlying neurological issues that can manifest in teenage/early adulthood years independently of drug use, although use of psychedelic drugs

Some people have underlying neurological issues that can manifest in teenage/early adulthood years independently of drug use, although use of psychedelic drugs does tend to exacerbate such problems. It is possible the drugs permanently changed this person. It is also possible the drugs merely accelerated what would have happened regardless. For most people, psychedelics are indeed pretty harmless.