Alcohol damages the brain more than cannabis, new research suggests.
Scientists at the University of Colorado Boulder conducted a review of existing imaging data that looked at the effects of alcohol and marijuana, or cannabis, on the brain.
They found unlike booze, marijuana does not affect the size or integrity of white or gray matter in the brain, even after years of exposure.
Study author Professor Kent Hutchison from the University of Colorado Boulder, said: "While marijuana may also have some negative consequences, it definitely is nowhere near the negative consequences of alcohol."
The scientists add, however, research into cannabis' mental effects are still very limited.
In the US, 44 percent of those aged 12 or over have used cannabis at some point in their lives.
Washington, Oregon, California, Alaska and Colorado have legalized marijuana for medical or recreational use.