Researchers have debated whether smokers of high-potency cannabis varieties are at greater risk of addiction because they get more THC, or if they compensate for the pot's strength by using or inhaling less of it.
That doesn't really matter, say the authors of the new report. Smokers of potent pot do get more THC than smokers of traditional varieties, they found. But it's their style of pot smoking that predicted who was most likely to become dependent.
"No drug use is without risk," said lead author Peggy van der Pol, a doctoral candidate at the Trimbos Institute of the Netherlands Institute of Mental Health and Addiction. "When using stronger cannabis you will likely take in more THC than when using less potent cannabis," she told Reuters Health in an e-mail.
Most previous research into cannabis dependence has looked mainly at how frequently a person uses cannabis, Van der Pol and her team note in the journal Addiction.
But the assumption that heavier THC exposure leads to greater addiction risk ignores the possibility that THC dose is not the main determinant of who becomes dependent, they write.
Van der Pol and her team analyzed data on 98 young adults taking part in an ongoing long-term study of frequent marijuana users in the Netherlands. The participants were recruited from coffee houses where the sale and use of cannabis is permitted and via referrals. Each person reported smoking marijuana on at least three days a week for more than a year.
At the start of the study, three quarters of the participants were men and 23 years old, on average. One in three met the criteria for marijuana dependence at that point.
A year and a half after recruitment, and then a year and a half after that, the participants were interviewed about their cannabis use and asked to smoke a joint in a comfortable setting while researchers documented details of their behavior. To simulate real-world conditions, smokers were asked to bring their own cannabis and to roll their own joints.
Contrary to the authors' original predictions, the smokers of the more potent pot varieties did not roll weaker joints. They used more cannabis in each joint than their peers who smoked lower-strength cannabis.
Smokers of potent varieties did inhale less smoke and they smoked at a slower pace than their peers, the study team found.
"Users seem to partly adjust, or 'titrate' their THC intake, but not sufficiently so to fully compensate for the THC-strength," van der Pol told Reuters Health. "So users of more potent cannabis are generally exposed to more THC."
These adjustments in smoking behavior may not be intentional, she added. "On average, users seem not to fully compensate for cannabis strength by inhaling less smoke. Yet, as the smoking behavior may be an unconscious process, users are likely unaware whether or not they (partly) compensate their intake."
Taking smaller and less frequent puffs on their marijuana joints did not appear to alter their risk of dependence either, the results indicate. The decreased volume of marijuana puffs - determined by a device that measured puff volume, duration, and related factors - and the total number of puffs was associated with more severe marijuana dependence, both at the start of the study and at follow up, the researchers note.
Total monthly exposure to THC did predict the severity of dependence at the three-year mark, but not independent of a person's dependence status at the beginning of the study.
Only smoking behaviors - like how much of a joint people smoked, or how frequently they puffed - predicted dependence at the three-year mark regardless of THC exposure or dependence status at the start, the researchers report.
Dr. Wilson Compton, Deputy Director of the National Institute on Drug Abuse (NIDA) told Reuters Health via e-mail, "This is an important study that helps to understand that increasing potency of marijuana may be related to increasing blood levels of THC, despite some reductions in how much people smoke when the marijuana is stronger."
Compton, who was not involved in the study, added, "this is an important area of research, and we do need a better understanding of it, but we remain concerned particularly for new and young users who may not titrate in the same way as experienced users, and thus may be exposing their brains to higher levels of THC from the outset."
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