At one hospital, the death rate after traumatic brain injury was lower among people who tested positive for tetrahydrocannabinol (THC, the active ingredient in marijuana) than among people who tested negative for it, researchers found.
“This data fits with previous data showing that (THC) may be neuroprotective,” Dr. David Plurad, one of the study's authors, said in a phone interview.
Experiments in animals have found that THC may protect the brain after injury, Plurad and his colleagues write in The American Surgeon. Little is known about the specific effects of THC on brain injury in humans, however.
For the new study, the researchers reviewed data on 446 adults treated at Harbor-UCLA Medical Center in Torrance, California for traumatic brain injuries. All had been tested for THC.
Overall, approximately one in five patients tested positive for THC and one in 10 patients died after their injury.
About 2.4 percent of people who tested positive for THC died, compared to about 11.5 percent of those with negative THC tests.
People who tested positive for THC were about 80 percent less likely to die, compared to people with negative THC tests, researchers found after they adjusted the numbers to account for age, gender, injury severity and type.
Previous studies have also suggested that alcohol may protect the brain in traumatic brain injuries, Plurad said. Those studies did not account for the presence of THC, however.
“We included the presence of alcohol in our statistical analysis, and it didn't turn out to be as protective as the presence of the marijuana,” he said, adding that future studies examining the effects of alcohol on traumatic brain injury should account for the presence of THC.
One concern with the study, according to Plurad, is that the test for THC could not distinguish occasional from regular users. A person could test positive after having used marijuana days or even weeks before.
Given that marijuana is inexpensive and may have some medical benefits, its therapeutic effects are worth investigating further, he added.
“There's not going to be one answer, is marijuana good for you, is marijuana bad for you,” he added. “Like most things in life, and particularly medicine, it's going to be somewhere in between.”