Marijuana Study Shows Brain Impairment In Young Adults

According to a marijuana study published in The Journal of Neuroscience even occasional recreational marijuana use has shown brain impairment in young adults and may lead to previously unidentified brain changes.

Marijuana use is often associated with motivation, attention, learning, and memory impairments. Previous studies exposing animals to tetrahydrocannabinol (THC) — the main psychoactive component of marijuana — show that repeated exposure to the drug causes structural changes in brain regions involved with these functions. However, less is known about how low to moderate marijuana use affects brain structure in people, particularly in teens and young adults.

“This study suggests that even light to moderate recreational marijuana use can cause changes in brain anatomy,” said Carl Lupica, PhD, who studies drug addiction at the National Institute on Drug Abuse, and was not involved with this study. “These observations are particularly interesting because previous studies have focused primarily on the brains of heavy marijuana smokers, and have largely ignored the brains of casual users.”

The More Marijuana The Greater The Abnormalities

The team of scientists involved in the study compared the size, shape, and density of the nucleus accumbens and the amygdala — a brain region that plays a central role in emotion — in 20 marijuana users and 20 non-users: “Each marijuana user was asked to estimate their drug consumption over a three-month period, including the number of days they smoked and the amount of the drug consumed each day.  The scientists found that the more the marijuana users reported consuming, the greater the abnormalities in the nucleus accumbens and amygdala. The shape and density of both of these regions also differed between marijuana users and non-users.”

The scientists suggest the study raises a strong challenge to the idea that casual marijuana use isn’t associated with bad consequences.

According to “Brain function depends on a complex interplay of chemicals known as neurotransmitters that act as carriers of information between cells called neurons. Tetrahydrocannabinol (THC), which is the main active ingredient in marijuana, affects this interplay by altering the strength of some of these signals. THC also interferes with the normal communication between neurons and between brain circuits. THC specifically interacts with brain proteins named cannabinoid receptors that are highly expressed in the brain. A higher density of these proteins exists in brain areas that are critical for learning, memory, pain perception, and reward processing. In fact, scientists think the activation of cannabinoid receptors in the brain’s reward pathways may underlie marijuana’s likelihood for abuse.”

Why This Marijuana Study Matters To South Africa

According to Medispace’s Dr.Tshidi Gule,  South Africa is considered the world marijuana capital. Statistics show that around eight percent of South Africans use the recreational drug, which is twice the global average.

Health experts like Dr. Gule are concerned about the rising levels of abuse of the substance by South Africans, particularly young adult males. Another danger cited is that marijuana is considered a gateway drug to much more serious drug types, such as heroin and cocaine.

Dr. Gule is against the call to legalise marijuana for medicinal use. Speaking to Longevity she said she did not support the call by the late MP for the Inkatha Freedom Party Dr. Mario Ambrosini, to liberalise medical treatment in terminal cases of cancers and other diseases, and to liberalise the medical, commercial and industrial use of marijuana.

Ambrosini claimed that it was a crime against humanity to deny the treatment to millions of cancer patients. Before he passed away he called for the decriminalisation of marijuana for medical and industrial purposes and said it was a huge opportunity for the country.

Dr. Gule believes South Africa is currently ill prepared to manage the legalization of the substance and says the risks to the greater population’s health far outweigh the suggested medical benefits.


Important References on the marijuana study:

This article is based on a release by The Journal of Neuroscience  which is published by the Society for Neuroscience, an organization of nearly 40,000 basic scientists and clinicians who study the brain and nervous system. Gilman can be reached at, Blood at, and Breiter at  More information on marijuana and addiction can be found on  This research was funded by the National Institute on Drug Abuse, the Office of National Drug Control Policy, Counterdrug Technology Assessment Center, and the National Institute of Neurological Disorders and Stroke.