Stoners out there who don't relate to what they read about marijuana's effects on the brain may be able to chalk up some of those differences to tobacco use.

Marijuana and tobacco are a popular pairing among pot users – researchers say that around 70 percent of marijuana users are tobacco users, too – but research has largely neglected this combination. It turns out that using both may be be better for brain function than using marijuana alone, a study published in the journal Behavioural Brain Research suggests.

"The combined use of marijuana and tobacco is highly prevalent. For instance, a 'blunt' is wrapped in tobacco leaf. A 'spliff' is a joint rolled with tobacco. We really need to understand how the combined use changes the brain to really understand its effects on memory function and behavior," Francesca Filbey, principal investigator of the study and director of cognitive neuroscience of addictive behaviors at the Center for BrainHealth, explained in a statement.

People who use either tobacco or marijuana alone tend to experience shrinkage of a brain region known as the hippocampus, which plays a central role in memory. The size of the hippocampus is directly correlated to memory function in people who don't use drugs, with memory function decreasing as the size of the hippocampus decreases.

Brain scans taken with magnetic resonance imaging (MRI) revealed that both substances shrink the hippocampus, too, but the researchers noticed a trend in users of both drugs that they didn't see in users of just one. Among users of both tobacco and marijuana, smaller hippocampus size was correlated with greater memory function. Users of only tobacco or marijuana exhibited no relationship between hippocampus size and memory.

"Our findings exemplify why the effects of marijuana on the brain may not generalize to the vast majority of the marijuana-using population, because most studies do not account for tobacco use. This study is one of the first to tease apart the unique effects of each substance on the brain as well as their combined effects," Filbey said in a statement.

Since scientists are only just beginning to explore the interactions between marijuana and tobacco, confirming this relationship will require further studies. But some diehard users would surely see this as reason to spark one in celebration.

Photo: Chuck Grimmett | Flickr