How common is HPPD?
No large-scale studies have been done, and so there is no definitive answer to this. Also, even the small amount of lab research which has been done has not been reproduced and verified by unrelated labs. It is likely that HPPD is under-reported because so few people in the medical community know what it is. Severe HPPD seems to be very rare although Dr. Abraham estimates the number may be as high as 1-5% of LSD users. This is his best guess based on his research experiences and the small studies which have been done, but the epedemiological studies to verify this have not been attempted. In ongoing research in collaboration with Erowid, Matthew Baggott and colleagues from University of California Berkeley found that HPPD-like symptoms occurred in 4.1% of participants (107 of 2,679) in a web-based survey of hallucinogen users. These 107 people reported psychedelic-related visual problems serious enough that they considered seeking professional help. Sixteen of the 107 had actually soug
