Even in clinical situations where cannabis is administered orally at low doses, psychotic reactions can occur, Swiss researchers report the current issue of BMC Psychiatry.

Recreational cannabis use has been associated with psychotic reactions, but this is the first such report in closely monitored subjects participating in a clinical trial, note Dr. Bernard Favrat and colleagues at Institut Universitaire de Medicine Legale in Lausanne.

Favrat’s group was conducting a study to examine the effects of ingestion of THC (delta-9-tetrahydrocannabinol) on psychomotor function and driving performance in eight occasional cannabis users.

The first case of psychosis was in a 22-year-old man given 20 milligrams of dronabinol, a synthetic THC. Ninety minutes after dronabinol administration he experienced severe anxiety and symptoms of psychosis, and was unable to perform the two psychometric tests.

Levels of THC and its active metabolite 11-OH-THC in the blood at the time of the strong adverse effects were 1.8 and 5.2 nanograms per milliliter, respectively.

The second case was also a 22-year-old man who developed severe anxiety one hour after taking 16.5 milligrams of a THC compound, when his THC blood level was 6.2 nanograms per milligram and 11-OH-THC was 3.9 nanograms per milligram. For several hours he was unable to perform psychometric tests

The authors note that Smoking a 3.5-percent marijuana cigarette leads to blood concentrations of THC in the range of 50 to 100 nanograms per milliliter. They believe that oral administration produces higher levels of 11-OH-THC, with slower elimination.

Alternatively, they suggest that “consuming oral cannabis may produce more potent, yet unknown psychotomimetic metabolites of THC.”

“Doctors and users should be aware of the increasing availability of oral cannabis in ‘special’ drinks or food as well as in medications under development,” which can result in “significant psychotic reactions,” Favrat’s group cautions.

SOURCE: BMC Psychiatry, April 1,2005.