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Could a marijuana-based medicine potentially prevent the symptoms of post-traumatic stress disorder (PTSD)? If the findings of a new study in rodents hold up, they may offer a new avenue for treatment of an illness that affects at least 7% of Americans during their lifetimes.
For the study, published in the journal Neuropsychopharmacology, researchers exposed rats to severe, Navy Seal-level stress, including restraint, forced swims and anesthetization. Luckier control rats just stayed in their cages and were handled twice by researchers.
Like humans who develop PTSD, the stress-exposed rats later became oversensitized to more moderately stressful stimuli, showing an exaggerated startle response to loud noises, for example. These rats also took longer to recognize that a once scary spot in a cage was now safe. Animals that had experienced traumatic stress also showed related changes in stress hormones.
But rats that were severely stressed, then immediately given a synthetic compound that mimics the effects of THC, the main psychoactive ingredient in marijuana, were mellower. They showed none of the stress-related changes seen in the rats receiving placebo.
The timing of the drug (known as WIN55, 212-2) mattered, though. The injections prevented symptoms of PTSD when they were given two or 24 hours after stress, but had no effect when administered 48 hours later.
The study, which involved a total of 637 male rats included in a series of 16 experiments, follows up similar previous work by the same author, this time using different tests of stress.
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So would smoking marijuana within a day of being exposed to trauma reduce the risk of PTSD is humans?
"I would not suggest smoking marijuana after a traumatic experience until we have controlled data from human studies," says lead author Irit Akirav of the University of Haifa in Israel, noting that it's clear that some people are already doing this in an attempt to self-medicate. (An FDA-approved drug called Marinol, which includes THC, already exists, so it could potentially be used in human trials.)
She cautions also that the THC in marijuana has what's called a biphasic effect, in which it can initially have one effect and later the opposite, so it could potentially backfire.
Further, while THC and WIN55, 212-2 both act on the same receptors in the brain, they do so to varying degrees, so it's unclear whether smoking marijuana would have the same effect as taking the experimental drug. And, of course, the effect of either drug on rats doesn't necessarily translate into humans.
Some veterans say medical marijuana helps treat their PTSD symptoms, but there has been no human research on the question. Some research in the addictions field has found an association between higher levels of cannabis use and increased PTSD, but this could simply reflect use of marijuana to self-treat PTSD.
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Interestingly, another controversial class of drugs may also have potential in preventing PTSD. Studies of both soldiers injured in combat and children suffering from severe burns have found that greater use of opioid drugs like morphine to treat their pain is associated with reduced risk of PTSD.
Given that higher doses of pain relievers are more likely to be given in cases of more severe injury — which may carry an increased risk for PTSD — the connection is notable.
Unfortunately, the politics surrounding drugs that are used recreationally means that interesting and possibly important compounds may be not be appropriately studied. Synthetic cannabinoids similar to WIN55, 212-2 (which cannot be used in humans) are often sold as "legal highs," which have led to bans by the Drug Enforcement Administration. Such bans reduce pharmaceutical company interest in developing potentially useful drugs because of the expense involved in studying controlled substances.
But since PTSD affects between 10% and 30% of people exposed to traumatic experiences including combat, rape, terrorism and natural disasters, a drug that could help prevent it could be remarkably helpful.
MORE: U.S. Rules That Marijuana Has No Medical Use. What Does Science Say?
Maia Szalavitz is a health writer at TIME.com. Find her on Twitter at @maiasz. You can also continue the discussion on TIME Healthland's Facebook page and on Twitter at @TIMEHealthland.
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