If you're referring mainly to marijuana, it's very well known that marijuana (and most other psychadelics) does not CAUSE permanent conditions such as HPPD, but rather, they bring those latent problems out and pronounce them. Thus, you always had HPPD, it was just never severe enough or pronounced enough for it to be a problem.
Hallucinogen persisting perception disorder, basically perpetual visual distortions like on a trip, except the trip is long over. But this normally results from the use of psychdellic/hallucigenic drugs, I'm sure weed didn't help, but I can't see this being caused by weed, unless you're one of the few lucky people who actually gets some good visuals when high.
