The present findings provide the first evidence that pre-extinction administration of THC facilitates extinction of conditioned fear in humans. In particular, participants that had received PBO during extinction learning exhibited spontaneous recovery of fear to a CS+ that was previously extinguished, whereas THC attenuated spontaneous recovery of fear. Of note, THC did not affect within-session extinction learning, but only influenced the ability to successfully recall extinction memory when compared to PBO, suggesting that THC affects the ability to maintain and/or successfully retrieve extinction memory. These findings are consistent with pre-clinical studies in rats in which cannabinoid activation and/or enhancement can lead to facilitation of extinction memory recall (Bitencourt et al., 2008; Chhatwal et al., 2005; Lafenetre et al., 2007; Lin et al., 2009; Lutz, 2007; Pamplona et al., 2008; Pamplona et al., 2006).
