Oral THC claimed to induce psychosis
A study by researchers of the University of Lausanne, Switzerland, on oral THC in eight healthy volunteers, of whom two developed psychotic reactions for some hours after ingestion, received some media attention. The press agency Reuters noted "Oral Cannabis Induces Psychosis at Low Levels". However, subjects did not receive low doses of THC and they did not develop a psychosis but psychotic reactions, such as anxiety and delusion, well known occasional side effects of cannabis ingestion.
Participants in the study were occasional users of cannabis and received either 20 mg of oral THC (Marinol) or an oral cannabis preparation containing either 15.8 or 45.7 mg THC on average. The study intended to investigate psychomotor impairment and driving capability after cannabis use. The two cases who developed psychotic symptoms were 22-year-old men who received 20 mg of THC or a cannabis preparation containing 16.5 mg THC. In both cases psychic side effects disappeared within several hours after ingestion.
Researchers expressed their surprise about the anxiety causing effects of THC which, however, are well known. Usually clinical studies start with single doses of 2.5 or 5 mg THC, rarely with 10 mg THC to find out the appropriate and tolerated dose and to avoid severe side effects. The tolerated doses vary considerably in different subjects. Only in regular users higher doses should be applied as starting dose. In recent clinical studies tolerated doses varied between 5 and about 100 mg THC daily.
(Sources: Reuters of 1 April 2005, BBC News of 1 April 2005, Favrat B, et al. Two cases of "cannabis acute psychosis" following the administration of oral cannabis. BMC Psychiatry 2005;5:17)