Parallel trajectories of vaping and smoking cannabis and their associations with mental and physical well-being among young adults.

Vaping and smoking are common modes of using cannabis (THC) among young adults, but little is known about how patterns of cannabis vaping and smoking unfold over time or how using one or both types of products may differently affect mental and physical well-being. This study examines parallel processes of cannabis vaping and smoking over 5 years and mental and physical outcomes in a sample of young adults. Annual surveys were conducted between 2016 and 2022 with a mostly California-based cohort of 2428 young adults. Parallel process growth mixture models examined trajectories of past-month frequency of cannabis vaping and smoking from ages 20 - 25. Classes were extracted based on parallel trajectories of vaped and smoked product use. Models assessed differences in self-reported mental (anxiety, depression) and physical (ailments, subjective overall) well-being outcomes in young adulthood across classes, adjusting for demographic characteristics and mental and physical well-being at pre-baseline (average age 19). Four cannabis vaping/smoking classes emerged: low use of cannabis (84.7%), decreasing smoking, low-moderate vaping (7.1%), stable moderate smoking, decreasing vaping (4.6%), and rapid increasing dual use (3.4%). Classes were similar on physical well-being indicators in young adulthood. The rapid increasing dual use class showed higher anxiety and depressive symptoms compared to other classes. Progression to higher frequency of both vaping and smoking cannabis in young adulthood may contribute to poorer mental well-being compared to other use patterns. Targeted efforts to reduce dual vaping and smoking in young people who use cannabis may be needed.