Long-term cannabis users in their twenties & thirties: where are they now?

Australian data from the National Drug Strategy Household Survey 2013 tells us that cannabis use is most prevalent among those aged 20-29 years, after which prevalence rates begin to steadily decline. Research over the last two decades also tells us that the two most important predictors of negative health outcomes associated with cannabis use are starting to use early (prior to 18 years) and using frequently. As such, it is not surprising that the majority of research on cannabis use as a whole has focussed on users who are younger than 30 years. In contrast, the relatively few studies involving users over 30 years have primarily focussed on treatment.

As Washburn and Capaldi (2015) rightly highlight, while we have an understanding of the variables associated with using cannabis for the first time and for continued use into our twenties, the pathways of further continued use during our thirties is not well understood. The key predictors of early use typically include antisocial behaviours (particularly conduct disorder), relationships with deviant peers and parents who use drugs, affective disorders and low parental monitoring. But, what about continued, long-term use?

Using data from the Oregon Youth Study, Washburn and Capaldi (2015) investigated the repeated assessment of a large sample of boys’ lives (across 26 years, starting at age 14) from a “bad neighbourhood” where the risk factors mentioned above were prevalent (n=205). This dataset was also unique in that it frequently included interviews with many of the participants’ families (a range of 182 [88%] to 188 [92%] mothers and 120 [59%] to 132 [64%] fathers participated). Using sophisticated analysis, the authors found that cannabis users where more likely to have parents who used during their adolescence and who did not monitor their behaviours. In contrast, adolescent factors such as affective disorder or antisocial behaviours were not significant predictors of cannabis use. One quarter of participants continued to use cannabis frequently during their twenties and were very likely to develop cannabis use disorder in their mid-twenties. This group also began to develop symptoms of depression and had more unstable relationships. In contrast, a total of 40% decreased their use and were more similar than different to the remaining non-users by their thirties. This group were not significantly more likely to be antisocial or deviant. Of note was that the risk factors of this group were not significantly different to the group of frequent long-term users.

In summary, this study had three important findings. First, parents’ behaviours play a key role in predicting their child’s decision to use cannabis. Whether or not the adolescent displayed other antisocial or deviant behaviours was less important. Second, one quarter of participants who used cannabis during their twenties would continue to use during their thirties at chronic, clinically significant levels. Third, risk factors for this group were not significantly different from the larger group of those who used in their twenties but decreased their use and became less likely to exhibit antisocial behaviours. As such, this study builds on previous evidence that, while the majority of users decrease their use from their twenties onward, there is a significant minority of users who continue frequent use even in their thirties. Most outstandingly, to decrease the chances of membership in this group a greater focus on parental behaviours is warranted above many of the behaviours of the adolescents themselves. Although it is not clear if this link is due to increased accessibility or genetic predisposition, the message is clear – keep an eye on your kids and be sure not to use cannabis near them!

Reference:

Washburn, I.J. & Capaldi, D.M. (2015). Heterogeneity in men's marijuana use in the 20s: Adolescent antecedents and consequences in the 30s. Development and Psychopathology 27, 279-291.