Though marijuana use has gone up sharply since 2007, claims about its lack of harm compared to cigarettes or drugs are not based on evidence. Instead, studies have shown abnormalities in brain function and structure of long-term marijuana users and that chronic marijuana users have smaller brain volume in the orbitofrontal cortex (OFC), a part of the brain commonly associated with addiction, but also increased brain connectivity.
But the effects of chronic marijuana use on the brain may depend on the age of first use and duration of use, according to researchers.