Recreational marijuana is legal in 19 of America’s states. Yet, just because this drug is becoming legal and more widespread doesn’t mean there aren’t side effects of prolonged use. There is growing evidence that the longer a person consumes marijuana, the more cognitive effects they’ll suffer. In fact, it’s thought that cognitive functions such as verbal recall, processing speed, and other high-level skills decline the longer you smoke marijuana.
What Is Marijuana?
Marijuana is often referred to as weed, cannabis, pot, and a host of other slang names. It is the dried flowers, stems, and leaves from the Cannabis indica or Cannabis sativa plant. Also known as “the gateway drug,” marijuana contains psychoactive compounds known as THC and cannabinoids.
This is the most commonly used addictive drug following alcohol and tobacco, and there is widespread use among younger people. In fact, according to the National Institute of Drug Abuse, over 11.8 million young adults use marijuana each year. And what’s worse, this is leading to an increased amount of teens between the grades of 8th and 10th using it. Alternately, the number of people who believe it to be ‘risky’ is decreasing.
Marijuana’s Effect on Cognitive Function
Scientists have conducted many studies looking into marijuana’s effect on cognitive function in humans throughout the years. Imaging studies on the brain have resulted in varying results. Some studies have found no notable differences in the brains of people who don’t smoke with that of those who do. However, other studies suggest that using marijuana regularly, especially in adolescence, can alter connectivity and reduce the volume of some brain regions.
Let’s take a closer look at a few of these studies:
Marijuana Exposure In Unborn Babies
A great deal of research shows that when humans are exposed to cannabis during development, it can lead to long-term changes in the brain. They found that rats exposed to THC before and shortly after birth and during adolescence show issues with certain memory and learning tasks later in life. Most of the cognitive impairment in the adult rats with adolescent exposure was found in their brain’s hippocampus. Further studies showed that these rats also had an impaired reward system in adulthood, which means they were more likely to seek out other harmful drugs.
New Zealand Long-term Marijuana Exposure Study
Several studies suggest that using marijuana long-term may cause decreased cognitive function, but the degree of the damage largely depends on when the person began using it, how much they use, and how they use it.
One such study in New Zealand tracked almost 4,000 young adults over a 25-year period. What they found was cumulative marijuana exposure resulted in lower test scores for verbal memory. However, they didn’t find any impairment with other abilities such as mental processes or processing speed. Yet, these effects were significant and sizable even when the researchers eliminated people still using and adjusted for other factors such as demographics, psychiatric conditions, and the use of alcohol and other drugs.
This study also found a link between marijuana use and IQ decline, especially among people who began smoking marijuana during their younger years. Yet, not all of these studies have drawn the same conclusions. The link between marijuana use and IQ decline is hard to prove. Other elements such as family environment, genetics, and marijuana use factors also play a role in declining IQ.
So, what did the New Zealand study conclude? They found that people who started smoking marijuana as adolescents lost between 6 and 8 IQ points by middle age. The people who used this drug heavily as teenagers but quit as adults never regained those IQ points. However, people who start using marijuana as adults didn’t lose any IQ points.
JAMA Internal Medicine Publication
The final study we’ll discuss today followed a group of people who began between the ages of 18 and 30. They studied these people initially and then again after 25 years had passed. They found that for every five years of marijuana use, the ability to recall common words declines.
At the 25 year checkup, they tested processing speed, verbal memory, and other high-level skills to determine how well these people’s brain regions worked together. Their initial tests showed that the longer a person uses marijuana, the worse they perform on all cognitive function tests. When accounting for other factors such as education level, they found that prolonged marijuana use basically affects verbal memory the most. For every five years of marijuana use, people recall one less word from a given list. The researchers plan to invite the participants back after the 30-year mark to perform more cognitive tests.