Written by Honor Whiteman, 29 November 2016

A new study warns that marijuana use may increase susceptibility to Alzheimer's disease, after finding the drug severely reduces blood flow in an area of the brain affected by the illness.

[A man smoking marijuana]
Researchers suggest marijuana use may increase susceptibility to Alzheimer's by reducing blood flow in the hippocampus.
Published in the Journal of Alzheimer's Disease, the study reveals that individuals with a marijuana use disorder showed reduced blood flow in nearly all areas of the brain, compared with healthy controls.

What is more, the research team - including co-author Dr. Elisabeth Jorandby of Amen Clinics Inc. in California - found that the hippocampus saw the largest reduction in blood flow with marijuana use.

The hippocampus is the brain region associated with learning and memory, and it is the first region to be affected in patients with Alzheimer's disease.

In the United States, marijuana is becoming increasingly legalized for recreational and/or medicinal use.With this in mind, researchers are in agreement that it is more important than ever to understand the possible harms of marijuana use, and Dr. Jorandby and colleagues caution that reduced brain blood flow may be one such effect.

Almost every brain region affected by marijuana use. When blood flow in the brain is reduced, this causes a reduction in the amount of oxygen that reaches brain cells, which can cause brain tissue damage and death.

According to the authors, few previous studies have assessed the effects of marijuana use on blood flow in the brain.

To address this research gap, the team used single photon emission computed tomography (SPECT) to measure the blood flow and brain activity of 982 individuals who had been diagnosed with a marijuana use disorder, alongside 92 healthy controls. SPECT was used to measure participants' brain blood flow and activity during a mental concentration task and when at rest.

Compared with the healthy controls, the researchers found that subjects with marijuana use disorders showed significantly reduced blood flow in almost all brain regions, but the hippocampus fared worst. In particular, the team identified abnormally low blood flow in the right hippocampus of subjects with marijuana use disorders as they completed the concentration task.

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