but only 35% of controls had a suprathreshold response to 2.5 mg Δ9-THC, and 75% of schizophrenic patients but only 50% of controls had a suprathreshold response to 5 mg Δ9-THC (Fig. 3). Similarly, relative to controls, schizophrenia patients were specifically more vulnerable to the dose-related learning impairments produced by Δ9-THC [44]. Under the influence of 5 mg Δ9-THC, schizophrenia patients (solid lines) showed no learning whatsoever (Fig. 2). Δ9-THC also increased the number of intrusions and false-positives generated during recall. Further, 5 mg Δ9-THC reduced learning and recall in healthy controls to the level of schizophrenia patients in the placebo condition. While admittedly speculative, perhaps greater group differences between schizophrenic patients and controls might have been observed if the patients were not taking antipsychotic medications and/or were not clinically stable.
