MINNEAPOLIS (AP) – Researchers from the University of Minnesota found that cannabis use had little effect on long-term cognitive abilities by tracking groups of twins from age 11 through adulthood.
Of 2,410 identical pairs of twins from Minnesota, only 364 had different cannabis use between siblings, so they were eligible for the study. The following twins enabled researchers to observe differences in cannabis use with fewer variables.
“The twin sample is representative of the population of the entire state of Minnesota,” said Dr. Steve Malone, study co-author and researcher at the Institute for Child Development (ICD). “But I think it’s a really important feature of the design that these samples are representative of the general population of us.”
Dr. Jonathan Schaefer, an ICD postdoctoral fellow at the university, joined the study two years ago. The university researchers Dr. William Iacono and Dr. Matt McGue started the study in the 1990s.
The ongoing study examines the cognitive, psychological, and socio-economic outcomes of cannabis use. The twins received a baseline assessment that included an electroencephalogram (EEG) every two years. The researchers also urge the pairs of twins to report themselves on topics such as the frequency of their cannabis use and the physical effects.
The twins are also tested for cognitive abilities through vocabulary, memory, and cognitive tests. The long-term cognitive differences were small, reported The Minnesota Daily.
Dr. Monica Luciana, psychology professor and research fellow, said the idea that adolescent cannabis use exacerbates mental health problems and cognitive impairments is a common perception.
“We came to the conclusion that there is little evidence that cannabis has dramatic effects on cognitive abilities, at least from adolescence to adulthood,” said Schäfer.
While the twins who use more cannabis meet the criteria for more mental health problems, perform worse on socioeconomic status, and score slightly lower on vocabulary tests, this is not directly related to cannabis use, Malone said.
Instead, the researchers’ results suggest that cannabis use can cause academic or motivational difficulties in adolescents that can affect a person’s educational and professional status later in life, he said.
76 percent of heavier twins who use cannabis continued their education beyond high school, compared to 82 percent of lighter or sober twins. The grade point average differs by an average of about 0.2 points between the two siblings.
At the beginning of the study, researchers focused on identifying factors that led to cannabis use. As the twins got older, researchers focused on observing the long-term effects of cannabis use. The study’s immediate focus changes to reflect concerns or issues relevant to the participants’ stage of life, Malone said.
“If you follow people long enough, you can really begin to examine the difference between early substance use and physical health outcomes,” Schäfer said. “Or even between substance use and signs of early cognitive decline.”
The researchers also worked with a complementary twin study at the University of Colorado Boulder, using the same set of twins that they have followed since the 1990s. The two studies are as symmetrical as possible to compare Minnesota with Colorado, a state that legalized recreational cannabis use, to observe the effects of legalization on substance use.
“There is a lot of interest these days, especially given efforts to legalize cannabis, how cannabis affects behavior, how it affects the brain, and especially whether its effects are more pronounced in some age groups compared to others,” said Luciana.
Schaefer said he would like to repeat the University of Minnesota twin study with a new group, using more recent data, to see if the changes in cannabis use since the 1990s, such as increased potency, dosage, and a variety of new forms, have had an impact.