Marijuana Addiction Alters Brain’s Normal Resting State


People addicted to marijuana and other forms of cannabis experience a significant decline in the strength of brain activity during moments of rest, according to new findings from a team of American scientists.

Public health officials and researchers know that marijuana’s increasingly benign popular reputation conflicts sharply with the drug’s potential to alter and damage brain function. In a study published in June 2015 in the journal Drug and Alcohol Dependence, researchers from the University of Pennsylvania assessed the impact that marijuana/cannabis addiction has on the brain’s baseline rate of activity while the body is at rest. These researchers concluded that cannabis addiction is associated with a meaningful decline in the strength of the connection between several important brain areas.

Cannabis Addiction

The cannabis plant is the source for marijuana (cannabis leaves and flowers) and two other drugs called hashish (concentrated cannabis resin glands) and hashish oil (hashish extracted with some form of solvent). All of these drugs contain THC (tetrahydrocannabinol) as their primary psychoactive ingredient. As a rule, marijuana contains less of this ingredient than hashish or hashish oil, although recent increases in marijuana potency have sharply diminished the differences between the mind-altering effects of the drug and the effects of hashish. Regardless of the type of cannabis under consideration, THC creates an addiction risk (especially in repeated users) by altering the normal levels of euphoria-producing chemicals in the brain’s pleasure center.

If you consume marijuana every day or almost every day, your lifetime chance of developing a cannabis addiction is roughly 25 percent to 50 percent, the National Institute on Drug Abuse reports. The lifetime addiction rate for teenagers who use the drug only casually or occasionally is 17 percent. When all age groups and usage levels are considered, lifetime rates for cannabis addiction stand at approximately 9 percent. The American Psychiatric Association reserves a diagnostic category called cannabis use disorder for all people addicted to cannabis, as well as all non-addicted cannabis users who engage in drug-based behavior that’s clearly harmful to the self or others.

Marijuana and Brain Function

Studies conducted on humans and test animals indicate that marijuana use can have a profoundly negative effect on long-term brain function. For example, teenagers who use the drug may experience potentially permanent alterations in their normal brain development. Middle-aged adults who began a pattern of regular marijuana consumption in adolescence have average IQ (intelligence quotient) scores that are roughly 8 points lower than their counterparts with no such early history of cannabis use. In addition to increasing the brain’s euphoria levels, THC can substantially alter memory formation in a brain area called the hippocampus. For this reason, habitual marijuana use may markedly increase the rate of memory loss associated with normal aging.

Addiction and the Brain at Rest

In the study published in Drug and Alcohol Dependence, the University of Pennsylvania researchers used a small-scale project involving 87 adults to assess the impact that cannabis addiction has on the strength of the brain’s connections while at rest. The researchers used this same project to assess the brain impact of nicotine addiction. Nineteen of the study participants were addicted to some form of cannabis but didn’t smoke cigarettes or any other form of tobacco. Another 23 participants had a cannabis addiction and also smoked, while 24 participants were nicotine addicts who didn’t use cannabis. The remaining 21 participants formed a generally healthy comparison group of people who didn’t consume cannabis or nicotine. In all four groups, the researchers used real-time brain imaging to examine the resting strength of the connections in the parts of the brain responsible for higher-level mental function.

The researchers concluded that the study participants addicted to cannabis had a significantly reduced level of brain connection strength when compared to the group of participants who didn’t consume cannabis or nicotine. This finding applied to the cigarette-using group of cannabis consumers, as well as the non-cigarette-using group of cannabis consumers. In addition, the researchers concluded that the participants who only smoked cigarettes also had a reduced level of connection strength in the brain areas under consideration.

The study’s authors found that some of the observed changes in brain connection strength were largely dependent on the amount of time over which the cannabis-addicted participants had consumed the drug. In other words, the addicted participants with longer histories of use had more signs of observable change than the addicted participants with shorter histories of use.

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