SAN FRANCISCO — As marijuana legalization continues to grow in the U.S. and more states discuss nixing laws and restrictions on use of the drug, an alarming study finds there might be good reason to put the breaks on easing legislation.

The study found abnormally low blood flow in the hippocampus — the portion of the brain paramount to memory and learning functions — among marijuana users, suggesting use of the drug might raise the risk of developing Alzheimer’s disease.

More than 26,000 people participated in the study, and nearly 1,000 of them were regular marijuana users. Researchers said the folks who used marijuana showed reduced blood flow in nearly all regions of the brain, but especially the hippocampus. Alzheimer’s disease attacks the hippocampus first as it grows in patients.

Published in the Journal of Alzheimer’s Disease, researchers studied participants’ brains using single photon emission computed tomography (SPECT), a sophisticated imaging study that evaluates blood flow and activity patterns.

“Prior papers have suggested that marijuana can damage the brain. What surprised [us] was how low blood flow was in the brains of our cohort – virtually every brain area had reduced blood flow on perfusion imaging in relation to marijuana use,” study co-author Dr. Cyrus Raji, of the University of California-San Francisco, tells Medical News Today.

Dr. Raji adds that frequent monitoring of patients prescribed medical marijuana by their doctors was “certainly worthy of careful consideration.”