However, DA D2 receptor antagonism fails to block Δ9-THC-induced c-fos expression in both the striatum and nucleus accumbens of rats [157]. Similarly, in humans, the DA D2 receptor antagonist haloperidol did not reduce any of the psychotomimetic, cognitive, and perceptual altering effects of Δ9-THC [45]. This is in contrast to the observation that haloperidol reverses the psychotomimetic effects of amphetamine [14]. In fact, haloperidol worsened some of the cognitive deficits produced by Δ9-THC. Collectively, these data suggest that it is unlikely that D2 receptor mechanisms play a major role in mediating the positive (psychotomimetic) effects of Δ9-THC.
