Co-use of cannabis, tobacco linked to poorer functioning among adults

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Washington DC: As cannabis is being legalised in more and more jurisdictions, more than a third of young adults report using both cannabis and tobacco or nicotine products, providing a unique challenge to public health officials, a recent study suggests. As part of the study, researchers examined the many different ways that cannabis and tobacco or nicotine products are used together -- a byproduct of the introduction of new vaping devices and other delivery methods.

Among those surveyed, young adults who used cannabis and tobacco or nicotine together in some way (either using one right after the other or by mixing the products together) tended to consume more marijuana and tobacco or nicotine products, and report poorer functioning and more problematic behaviours compared to those who used did not use both products together.

"There is growing concern that as more states legalise marijuana, there also will be an increase in tobacco use because the two substances may be used together. Co-use of cannabis and tobacco could reverse some of the progress made on reducing rates of tobacco use," Joan Tucker, lead author of the study published online by the journal Psychology of Addictive Behaviors.

Mixing cannabis and tobacco is more common in some other countries compared to the U.S. But in recent years, cannabis and tobacco or nicotine co-use in the U.S. has risen among adults, coinciding with greater availability and diversity of cannabis, tobacco and vaping products. In the U.S., national data show that young adults between the ages of 18 and 25 are more likely to use cannabis, tobacco or nicotine products than any other age group.

Studies on the issue thus far have been limited in scope. They typically have not accounted for the use of newer vaping products nor examined whether certain ways of co-using these substances is associated with greater problems. As part of the study, researchers surveyed more than 2,400 young adults during 2017 and 2018. Participants have taken part in an ongoing study of substance use patterns from adolescence to young adulthood. While they originally were recruited in 2008 from 16 middle schools across Southern California, they now live in more than 400 neighbourhoods throughout the state.

Among the young adults in the survey, about half reported using cannabis during the past year, and 43% reported using some type of tobacco or nicotine product during the same period. About 37% reported co-use of the substances at some point during the past year. More than 80% of the young adults who reported past-year marijuana use also reported past-year tobacco use.

Using both substances sequentially (one right after the other) on the same occasion was reported by 17% of the young adults, and 14% reported using the substances together by mixing them in the same device. The study found that co-use of cannabis and tobacco or nicotine is associated with worse functioning, including poorer mental and physical health, as well as greater problematic behaviours such as fighting, skipping school, being fired and getting in trouble with the police.

Young adults who used both products in the past year, but did not use them on the same occasion, did not show greater risk compared to those who used only one of these products. "How these products are used together matters in terms of potential health consequences and functioning among people in their late teens and early 20s. Our findings suggest that we can no longer just think about the consequences of tobacco use or marijuana use alone -- we have to think about them together," said Tucker. With this study, the researchers seek to actively improve the health, social and economic well-being of populations and communities throughout the world.

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