Brain Study Explores Effects of Combined Use of Cannabis, Nicotine

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Those who use both nicotine and cannabis showed more brain connectivity than users of only one of the substances, according to new research at the Center for BrainHealth. 

Researchers at the Center for BrainHealth at The University of Texas at Dallas have found that the concurrent use of cannabis and nicotine has a different effect on brain connectivity than using only one of the substances.

In a study recently published in the journal Brain Structure and Function, the functional brain connectivity in individuals using both drugs more closely resembled that of nonusers. The nicotine-only and cannabis-only users showed equally less connectivity in general.

“Most of the literature to date has focused on associations of isolated cannabis and nicotine use, even though concurrent cannabis and nicotine use is more prevalent in society than cannabis use alone,” said Dr. Francesca Filbey, the study’s lead author and the Bert Moore Chair in BrainHealth at UT Dallas. “Our findings confirm the limitations of existing research.”

Separate regions of the brain can be functionally connected — meaning they exhibit similar activity — even if the regions are not physically connected. Differences in such brain network connectivity suggest alterations in the underlying neural architecture of the brain that supports brain function. Overall, Filbey said the study suggests unique and combined contributions of cannabis and nicotine on brain network connectivity, which may be helpful knowledge for intervention programs.

Previous research has suggested that nicotine may be a gateway drug leading to cannabis and other drug use. Studies performed elsewhere with rats exposed to THC — the main psychoactive compound found in marijuana — demonstrated an increased likelihood to self-administer nicotine that was not observed with rats exposed to heroin or cocaine, suggesting that there is something distinctive about the cannabis-nicotine interaction.

Dr. Francesca Filbey

In the new UT Dallas study, MRI scans were used to evaluate resting-state functions in 12 different regions of the brain among four groups of participants: 28 nicotine users, 53 cannabis users, 26 users of both substances, and 30 nonusers.

The scans revealed that nonusers displayed greater connectivity in almost all of the networks compared to the nicotine-only and cannabis-only groups. The nicotine-cannabis group had greater connectivity than the nicotine-only and cannabis-only groups. Notably, the study did not demonstrate a correlation between substance use severity and functional connectivity.

While the results of the study could be in part due to the opposing effects that nicotine and cannabis have on the brain, the differences in the participants’ brain connectivity highlight the need for further research, Filbey said.

In another recent study, researchers in Filbey’s lab found that cannabis users experience increased cortical activation and communication during the brain’s resting state when compared with nonusers.

The resulting “noisy brain” might impair brain activity and disrupt cognitive processes, said Dr. Shikha Prashad, a Center for BrainHealth research scientist and the lead author of the second study, published in the journal NeuroImage.

Both studies were funded by the National Institutes of Health.

Media Contact: The Office of Media Relations, UT Dallas, (972) 883-2155, [email protected].

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