tography), perceptions of entire objects, po sitive afterimages (i.e., a same-colored or
complementary-colored “shadow” of an object remaining after removal of the object), halos
around objects, or misperception of images as  too large (macropsia) or too small (micropsia).
Duration of the visual disturbances may be ep isodic or nearly continuous and must cause
clinically significant distress or impairment in social, occupational, or other important areas
of functioning (Criterion B). The disturbances may last for weeks, months, or years. Other
explanations for the disturbances (e.g., brain lesions, preexisting psychosis, seizure disor-
ders, migraine aura without headaches) must be ruled out (Criterion C).
Hallucinogen persisting perception disorder  occurs primarily after LSD (lysergic acid
diethylamide) use, but not exclusively. There does not appear to be a strong correlation be-
tween hallucinogen persisting perception disord er and number of occasions of hallucino-
gen use, with some instances of hallucinogen  persisting perception disorder occurring in
individuals with minimal exposure to hallucinogens. Some instances of hallucinogen per-
sisting perception disorder may be triggered by use of other substa nces (e.g., cannabis or
alcohol) or in adaptation to dark environments.
Associated Features Supporting Diagnosis
Reality testing remains intact in individuals with hallucinogen persisting perception dis-
order (i.e., the individual is aware that the disturbance is linked to the effect of the drug).
If this is not the case, another disorder might better explain the abnormal perceptions.
Prevalence
Prevalence estimates of hallucinogen persisting perception disorder are unknown. Initial
prevalence estimates of the disorder among individuals who use hallucinogens is approx-
imately 4.2%.