Researchers aimed to settle the economic debate of whether alcohol and cannabis act as substitutes or complements to one another. If substitutes, factors that limit availability of one substance lead to increased use of the other. For example, increased pricing of alcohol may lead individuals to use cannabis as a substitute. On the other hand, a complementary relationship is one in which factors that influence the availability of one substance has a parallel effect on the use of another substance. An example of this relationship would be an increase in alcohol consumption as a result of cannabis decriminalization.  Researchers recruited 876 college students that use alcohol and cannabis to participate in the daily diary study and report their proclivity to use alcohol or drugs to cope with stress, as measured by the 60-item COPE Inventory. The study found that levels of evening alcohol use were positively associated with the likelihood of cannabis use, indicating a complementary relationship between the two. However, individuals with stronger alcohol/drug coping tendencies showed a negative relation between evening alcohol use and cannabis use, having used alcohol and cannabis as substitutes rather than complements.

Take away: This relationship is important to understand as it is a key in developing public health interventions and policies that influence substance use. Higher levels of alcohol consumption predict higher odds of cannabis use in the college student population—unless the student is using alcohol as a coping mechanism, in which case the opposite effect occurs. This is important to keep in mind because policies or interventions developed with the intent to curb alcohol consumption might produce unintended results in certain groups of people, and could in fact drive an increase in cannabis consumption among students that use alcohol and cannabis as substitutes.

O’Hara, R.E., Armeli, S., & Tennen, H. (2016). Alcohol and cannabis use among college students: Substitutes or complements? Addictive Behaviors, 58, 1-6.