Age-Varying Prevalence of Marijuana and Opioid Use in the United States during 2001-2002 and 2012-2013

In the past decade, use of opioids and marijuana has become an increasing area of focus due to shifts in use, attitudes, and policies. Twenty-nine states have legalized use of marijuana in some form, including several states which legalized recreational use starting in 2012. Use of prescription opioids has risen dramatically since the late 1990s, and opioid overdose is now the leading cause of accidental death (Paulozzi et al., 2011; CDC, 2014). Many studies have documented the age-varying nature of substance use behavior; however, less is known about how age-varying rates of these behaviors may have changed over this period of upheaval in the substance use landscape.

Method. We used data from two nationally representative datasets of U.S. adults, NESARC I (N= 40,093, collected during 2001-2003) and NESARC III (N= 36,309, collected during 20012-2013). We used weighted time-varying effect modeling (TVEM, Tan et al., 2012) to flexibly estimate prevalence of past-year marijuana use and prescription opioid use from ages 18-90 for the two NESARC cohorts.

Results. Overall prevalence of use of both substances more than doubled from NESARC I to NESARC III (4.1 to 9.6% for marijuana and 1.8% to 4.1% for opioids). Results from TVEM demonstrate that at most ages across the adult lifespan, individuals in NESARC III reported a higher prevalence of both behaviors compared to NESARC I participants; however, the historical difference in rates of opioid use was significant only among adults older than about age 22. For both substances, prevalence of use was highest for NESARC I participants aged 18, declined sharply through the twenties, and then continued to decline after age 30. In NESARC III, use of both substances peaked several years later (in the early twenties), and declined with age. However, a second peak for opioid use was observed for NESARC III participants in the early fifties, with nearly 5% of NESARC III participants using opioids at this age, compared to less than 2% of those in NESARC I.

Discussion. Findings show an increase in both marijuana and opioid use across the past decade, with higher prevalence for the more recent cohort at nearly all ages across the adult lifespan. Consistent with prior research showing lower prevalence of substance use at older ages, use of both substances generally declined with age for both cohorts, although the more recent cohort shows some evidence of increased opioid use at older ages. Findings provide information about historical shifts in age-varying rates of substance use, which can be used to identify emerging public health needs and inform targeted prevention programs.