The effect of delta 9-tetrahydrocannabinol on the extinction of an adverse associative memory.

The cannabinoid Delta(9)-tetrahydrocannabinol (Delta(9)-THC) is currently being employed or tested for a number of therapeutic uses. Cannabinoid CB1 receptors are critically involved in adverse memory extinction. It is not known whether an unintended effect of Delta(9)-THC is increased extinction rates of adverse memories. We therefore tested the effect of Delta(9)-THC on adverse memory extinction using an auditory-stimulus/foot shock paradigm. We found that repeated administration of a high dose of Delta(9)-THC over 6 days retarded extinction compared with controls. This is in contrast to other reports and might be a result of endocannabinoid signalling dysfunction due to cannabinoid receptor densensitization.