Prevalence of hallucinations and their pathological associations in the general population.

Hallucinations are perceptual phenomena involved in many fields of pathology. Although clinically widely explored, studies in the general population of these phenomena are scant. This issue was investigated using representative samples of the non-institutionalized general population of the United Kingdom, Germany and Italy aged 15 years or over (N=13,057). These surveys were conducted by telephone and explored mental disorders and hallucinations (visual, auditory, olfactory, haptic and gustatory hallucinations, out-of-body experiences, hypnagogic and hypnopompic hallucinations). Overall, 38.7% of the sample reported hallucinatory experiences (19.6% less than once in a month; 6.4% monthly; 2.7% once a week; and 2.4% more than once a week). These hallucinations occurred, (1) At sleep onset (hypnagogic hallucinations 24.8%) and/or upon awakening (hypnopompic hallucinations 6.6%), without relationship to a specific pathology in more than half of the cases; frightening hallucinations were more often the expression of sleep or mental disorders such as narcolepsy, OSAS or anxiety disorders. (2) During the daytime and reported by 27% of the sample: visual (prevalence of 3.2%) and auditory (0.6%) hallucinations were strongly related to a psychotic pathology (respective OR of 6.6 and 5.1 with a conservative estimate of the lifetime prevalence of psychotic disorders in this sample of 0.5%); and to anxiety (respective OR of 5.0 and 9.1). Haptic hallucinations were reported by 3.1% with current use of drugs as the highest risk factor (OR=9.8). In conclusion, the prevalence of hallucinations in the general population is not negligible. Daytime visual and auditory hallucinations are associated with a greater risk of psychiatric disorders. The other daytime sensory hallucinations are more related to an organic or a toxic disorder.