The question of whether alcohol or marijuana is more damaging to users’ health has long been the subject of debate.
Scientists at the University of Colorado Boulder have added to the discussion with a new study indicating that alcohol, rather than marijuana, has more significant long-term effects on the brain.
The research, which was published in the journal Addiction, examined the brains of more than 1,000 participants of varying ages. The findings connect alcohol consumption with long-term changes to the structure of white matter and gray matter in the brain. The use of marijuana, however, appeared to have no significant, long-term effects on the structure of brain matter.
Study leader Rachel Thayer, of the Department of Psychology and Neuroscience at the University of Colorado-Boulder, and colleagues conducted a review of existing imaging data to compare the effects of alcohol and cannabis on the brain.
Study co-author Kent Hutchison, also of the UC-Boulder Department of Psychology and Neuroscience, said previous brain studies looking at the effects of alcohol and cannabis have yielded mixed results.
“When you look at these studies going back years, you see that one study will report that marijuana use is related to a reduction in the volume of the hippocampus. The next study then comes around, and they say that marijuana use is related to changes in the cerebellum… The point is that there’s no consistency across all of these studies in terms of the actual brain structures.”
Based on prior research, alcohol use severity is associated with widespread lower gray matter volume and white matter integrity in adults, and with lower gray matter volume in adolescents, the researchers noted.
Hoping to provide some clarification, Hutchinson, Thayer and their colleagues analyzed brain imaging data to find out how marijuana use affects white matter and gray matter in the brain, and how those effects compare with those caused by drinking alcohol.
Gray matter, the pinkish-gray tissue on the brain’s surface, mainly consists of neural cell bodies. White matter is the deeper brain tissue that transmits electrical impulses to other cells and tissues. Any reduction in the size of white or gray matter or a loss in their integrity can cause impaired brain function.
Scientists know less about cannabis’ effects on the brain than alcohol’s, due to a relative lack of research. “With alcohol, we’ve known it’s bad for the brain for decades,” Hutchison said. “But for cannabis, we know so little.”
The UC-Boulder study used the brain images of 853 adults aged between 18 and 55 years and 439 teenagers between the ages of 14 and 18. All participants varied in their use of alcohol and marijuana.
The researchers found that alcohol use — especially in adults who had been drinking for many years — was associated with a reduction in gray matter volume, as well as a reduction in the integrity of white matter.
Marijuana use, however, appeared to have no impact on the structure of gray or white matter in either teenagers or adults.
Based on these findings, the researchers believe that drinking alcohol is likely to be much more harmful to brain health than using marijuana. Regarding any possible benefits of marijuana use, however, Thayer and her team said much more research is needed to reach conclusions. “Research is still very limited in terms of whether marijuana use is harmful, or beneficial, to the brain.”
Both alcohol consumption and pot smoking can have negative health effects. However, alcohol has been linked to an estimated 88,000 deaths per year, according to the CDC, while there is no data on cannabis use and mortality. And research into marijuana’s health effects is still in its infancy, compared with a greater body of studies looking at alcohol and human health.
Marijuana is the most commonly used illicit drug (an estimated 22.2 million people have used it in the past month) according to the National Survey on Drug Use and Health.