I've had visual snow as long as I can remember, long before I tried any drug.
But drugs definitely increased the prevalence of HPPD, ever since I used cannabis and psychedelics the intensity and complexity of my HPPD have increased.
My symptoms usually peak in periods moderate psychedelic use, when pausing the use for months on end the symptoms decrease so much so that I forget that they're even there to begin with. Stress and sleep deprivation seem to increase these symptoms too.
EDIT: RIP gravedig lol