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Adolescents are More Sensitive to THC than Adults, Study Finds

By Alexander Beadle

Published: Apr 22, 2022   

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Adolescents are More Sensitive to THC than Adults, Study Finds

While adolescents may not feel any more intoxicated than their adult counterparts when given the same amount of THC, a new study suggests that their behaviors are impaired to a greater degree.

Published in the Nature journal Neuropsychopharmacology, the research from scientists at the University of Chicago used cardiovascular measurements and electroencephalogram (EEG) brain activity monitoring to study the health of adolescents and adults while they performed various cognitive tasks under the influence of THC.

While both groups reported similar feelings of intoxication and produced similar cardiovascular measurements, the adolescents showed greater cognitive impairment when carrying out the tasks. EEG measurements also found that THC dose-dependently affected the brainwave activity of adolescents, but not the adults.

These results could have important cannabis policy implications, the researchers say, as tasks such as driving could be more dangerous for young people driving under the influence.


Teens are more susceptible to cognitive impairment

The study consisted of twelve adolescents aged between 18 and 20 and twelve adults between 30 and 40. All were very occasional cannabis users, reporting no more than 20 lifetime uses of the drug with none in the last 30 days.

“It became clear to me that cannabis is greatly understudied,” study first author Conor Murray, a former UChicago postdoctoral fellow who is now at UCLA, said in a statement. “I wanted to understand what exactly the drug does to the brain and cognition, to what extent those effects represent an enhancement or impairment of cognition and awareness, and in which individuals they are most pronounced.”

The participants’ brain activity, blood pressure, and heart rate were measured while they remained at rest, and then while they attempted several attention-demanding cognitive assessment tasks. The researchers found that THC dose-dependently increased attention lapses and introduced feelings of time dilation in the adolescents, but not the adults.

“We actually had to remove one of the adolescents from analysis because they were so intoxicated they could not proceed with the task,” Murray added.

With the exception of that one participant, both the adolescent and adult groups still self-reported similar feelings of intoxication when surveyed. Heart rate measurements were raised in both groups after taking THC, but there was no significant difference in this increase between the groups.


THC affects alpha brainwave activity in teens, but not adults

To gather EEG data, each participant had 128 electrodes placed around their head. These electrodes pick up on the tiny electrical charges resulting from brain activity and can be interpreted to study what is happening in the brain at a given moment.

Different brainwave frequencies are known to be associated strongly with certain behaviors. For example, alpha waves are a mid-range frequency of brainwave that are known to be strongest during relaxation or other periods with low sensory input, such as when the eyes are closed. Their production requires synchronous activity between the neurons – “Like all the neurons are in a choir singing the same song,” Murray explained. 

“Like they’re all at rest, saying, ‘Om’. But as soon as they need to do a job, like making sense of the visual field when you open your eyes, they start chattering with each other – you can’t hear the synchronous activity anymore.”

The researchers found that the adults had less alpha power at rest than the adolescents, regardless of drug usage.

“My interpretation is that as you become an adult, you’re able to carry on individual conversations between neurons much more readily,” said Murray.

THC had no observable effect on the brainwaves at rest. But when performing the cognitive tasks, the adolescents were found to have significantly more trouble breaking out of the alpha wave state to properly focus on the task at hand. This was seen in attention tasks, as well as ones requiring quick recall, rapid reactions, and in the time dilation assessment.

“THC forces them to remain in a trance-like, meditative state,” said Murray.

THC also dose-dependently reduced the amplitude of the event-related potential (ERP) component P300 – which is known to be a valid index of attention and cognition – in the adolescents but not the adult group.

This study does have some important limitations. Most notably, the sample size was relatively small, and was not powerful enough to examine if there might be any additional sex-related differences between the male and female participants in their age-related responses to THC. The doses of THC used in the study were also lower than many of the THC products currently available on the consumer market, and so it is unclear what differences even more potent cannabis may elicit between age groups.


THC and the developing brain

Other research suggests that adolescent cannabis use may also actively change the structure of the developing brain.

A recent European brain imaging study involving 799 teenagers found significant associations between cannabis use and cortical thickness. More specifically, the left and right prefrontal lobes of teen cannabis users were thinner on average than those of their peers who had never used the drug. These brain regions are responsible for proper motor function, problem solving, and memory, underlying the importance of this finding.

Early animal studies have also suggested that teen cannabis use may alter the development of brain regions responsible for decision-making, planning, and self-control. Laboratory rats given THC during their adolescence showed reduced development of a support structure called the perineuronal net, which forms a lattice of proteins around inhibitory cells and helps to secure their connection with brain neurons and to regulate prefrontal cortex activity.

 

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