Abstract

Extremely small doses of lysergide (lysergic acid diethylamide, LSD 25) have profound effects upon mental function: 50 micrograms by mouth are active in most subjects. The effects include psychological disturbances and the development of impressive changes in perception, including visual hallucinations.¹ The ‘model psychoses’ induced by the drug have been experimentally investigated in the hope of clarifying the nature of psychotic illness by analogy. It may be relevant that lysergide powerfully antagonises the action of serotonin in the brain,² but psychosis is not simply due to disturbance of serotonin metabolism,³ nor does the mental state produced by lysergide much resemble that due to schizophrenia.⁴ The drug has been used as a diagnostic aid in doubtful cases of schizophrenia,⁵ but further work is necessary to confirm its usefulness for this purpose.