As the use of marijuana increases nationwide, another study is out showing the dangers of the so-called “harmless” drug. Marijuana can reduce blood flow to nearly all areas of the brain — and over the long term, put users at increased risk for dementia and Alzheimer’s disease.

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With so many more people using recreational and medicinal marijuana today, health officials, addiction specialists, researchers, and even some users are urging the public to better understand the potential harm.

The latest study points out there is significantly reduced blood flow to all areas of the brain, and specifically the hippocampus, when marijuana is consumed. The hippocampus is an area of the brain known to be affected by Alzheimer’s pathology. Reduced flow to any region of the brain can cause both tissue damage and death.

Researchers made the discovery using single photon emission computed tomography (SPECT). It looked at the blood flow and brain activity of 982 individuals who had been diagnosed with a marijuana use disorder, alongside 92 healthy individuals.

The media have given the general impression marijuana is a safe recreational drug.

“Our research demonstrates that marijuana can have significant negative effects on brain function,” said Daniel Amen, M.D., founder of Amen Clinics in California, in a statement. “The media has given the general impression that marijuana is a safe recreational drug; this research directly challenges that notion. In another new study just released, researchers showed that marijuana use tripled the risk of psychosis. Caution is clearly in order.”

The latest findings come on the heels of another study showing that smoking pot may affect your coordination and other motor skills — even when you’re not high.

And an extensive report earlier this month from the U.S. surgeon general outlined a mounting body of scientific evidence highlighting the dangers of marijuana use to not only individuals, but also to public health and safety.