Adolescent Marijuana Use Affects Brain Development

Connie K. Ho for — Your Universe Online
Researchers recently found that, for those who use marijuana in a persistent and dependent manner before 18 years of age, there will be lasting harm to the attention and memory of that individual.
The long-range study was conducted by scientists from Britain and the U.S., along with assistance of a cohort of over 1,000 New Zealanders in a 40-year period. These participants began to use cannabis when they were young children and used it consistently for years afterward. The researchers determined that there was an average drop of 8 points in IQ when IQ tests at age 13 and age 38 were compared. They also believe that quitting the habit didn´t reverse the loss.
“It’s such a special study that I’m fairly confident cannabis is safe for over-18 brains, but risky for under-18 brains,” Terrie Moffitt, a psychology and neuroscience professor at King´s College London´s Institute of Psychiatry, told Reuters.
The results, recently published online edition of PNAS, show how an important factor is the age at which the participants´ starting using marijuana and the brain´s development in relation to the drug use. Participants who didn´t start using marijuana until after they were adults with fully formed brains didn´t show the same mental decline as individuals who used marijuana early on. The researchers believe that, before age 18, a person’s brain is still developing and can have greater damage from drugs.
“Marijuana is not harmless, particularly for adolescents,” commented lead researcher Madeline Meier, a post-doctoral researcher at Duke University, in a prepared statement.
The study included psychological tests that examined memory, reasoning, processing speed, and visual processing. The participants who used marijuana as teens on a continuous basis tested lower on exams. As well, friends and family members were interviewed in the study and noted that persistent pot users had problems like losing focus and difficulty remembering to complete particular tasks.
“Many people today, especially young people, believe that marijuana is risk free, but this research tells us that this is not the case,” remarked Laurence Steinberg, a Temple University professor of psychology unaffiliated with the study, in a WebMD article.
In the group, approximately five percent were thought to be marijuana-dependent or categorized as using marijuana more than once a week before they turned 18. The researchers defined dependency as continuously using the drug even with health, family, or social issues at hand. As well, the researchers do not attribute the drop in IQ points due to other drug and alcohol use or less education. In general, higher IQ generally relates to more education, better health, and increased longevity.
“Somebody who loses 8 IQ points as an adolescent may be disadvantaged compared to their same-age peers for years to come,” explained Meier, who produced the results from the long-term Dunedin Multidisciplinary Health and Development Study, in the statement.
Furthermore, medical experts note that this is the first study to examine the IQ before and after the long-term use of marijuana.
“This strengthens the argument against adolescents using this drug,” noted Wayne Hall, researcher at the University of Queensland in Australia, in the WebMD article.
As well, researchers addressed how other animal studies with alcohol, cocaine, and nicotine have shown how similar harmful exposure to the brain can lead to long-term damage and more dependence.
“This study points to adolescence as a time of heightened vulnerability,” commented Steinberg in the statement. “The findings are pretty clear that it is not simply chronic use that causes deficits, but chronic use with adolescent onset.”
However, the scientists still do not know what the safe age is for marijuana use and how much pot dosage can lead to brain damage.
“The simple message is that substance use is not healthy for kids,” explained Avshalom Caspi, a researcher from Duke´s Institute for Genome Sciences and Policy, in a statement. “That’s true for tobacco, alcohol, and apparently for cannabis.”
In closing, more research is needed to confirm the findings of the study.
“Although one should never by convinced by a single study, I take the findings very seriously,” concluded Dr. Robin Murray of Kings College in the WebMD article.