Extinction usually means something is gone and it ain’t coming back. But for those who suffer from post-traumatic stress disorder (PTSD), “extinction” means learning new, positive information that wipes out the negative fears resulting from a previous traumatic experience. According to a Yale University professor of psychiatry, medical marijuana can amplify such "extinction learning." Military vets are the most visible group dealing with PTSD. It affects an estimated 600,000 vets – 40 percent of all returning soldiers – and its symptoms can last for years.

Yale's R. Andrew Sewell actually received permission from the feds to test THC on military vets suffering intractable PTSD. Prof Sewell's ongoing, multi-year study entitled "Cannabinoid Augmentation of Extinction Learning" was presented at the April 2013 Multidisciplinary Association for Psychedelic Studies (MAPS) conference in Oakland, CA. Professor Sewell theorizes that THC enhances "exposure therapy," which he regards as the most efficient treatment for PTSD. However, for many, exposure therapy is too painful to maintain because it forces the patient to continually revisit trauma memories until rendered less devastating.    

Sewell tested 60 PTSD vets and 60 healthy individuals as part of a control group, subjecting all subjects to electrical "shocks" whenever they saw a particular pattern. But after Sewell removed the shocks, the control group naturally relaxed when seeing the pattern again – but the PTSD patients could not, still anticipating a shock coming. The vets then got injected – and altered their consciousness – with one milligram of THC. It calmed them down sufficiently to realize they wouldn't be shocked further – extinction learning in practice.  

Prof Sewell theorizes that pot acts on the cannabinoid CB1 receptor; in previous studies, disabling CB1 receptors in shocked mice and apes rendered them permanently afflicted with PTSD. But activating the CB1 receptor with THC boosts extinction learning in lab animals.

Of course, thousands of vets already self-medicate their PTSD with pot, albeit illegally. Dr. Sewell's research adds a U.S. government sanctioned, clinical justification that could eventually aid most, if not all afflicted with the debilitating anxiety disorder.