Comment on Karriker-Jaffe et al.

In their article, Karriker-Jaffe, Subbaraman, Greenfield, and Kerr (2018) assess the contributions of heavy drinking, drug use and simultaneous co-use of alcohol and drugs to alcohol-use disorder (AUD) and drug abuse (DA). It was expected that simultaneous co-use would increase the risk for both AUD and DA, but in the end it was found to be strongly associated with DA only. However, according to the findings, co-use of alcohol and drugs may be an important risk factor for substance-use disorders, and therefore healthcare providers should screen for simultaneous co-use of alcohol and drugs to help identify patients who may benefit from substance-abuse treatment.

When studying polydrug use and its consequences, the measurements matter. Although polydrug use has been noted both in public discussions and in research for quite a while already, rather little effort has been put into developing its measures, for example in population surveys (Karjalainen, Kuussaari, Kataja, Tigerstedt, & Hakkarainen, 2017). Very often concurrent polydrug use (CPU) – the use of two or more different substances in a given time period, such as during the last 30 days or the last 12 months (Martin, 2008) – is applied as a measure. Questions about last-month or last-year prevalence of different kinds of substances are often readily available in different surveys, and therefore easy to use in order to measure polydrug use. However, CPU as a measure has been criticised, since the estimations vary widely according to the time period chosen and it may not depict the essence of the phenomenon that well, since there is no information about whether the effects of different substances used overlap or not (Karjalainen, Kuussaari, et al., 2017).

Simultaneous polydrug use (SPU), on the other hand, refers to the use of two or more substances at the same time or in temporal proximity (Martin, 2008). There is evidence that at least some forms of simultaneous polydrug use, e.g., alcohol and non-medical use of prescription drugs, would be a greater risk factor for mental, social and health issues compared to concurrent use (Baggio et al., 2014). As such, simultaneous polydrug use is a more recommendable measure to apply, especially from the point of view of harms and risks caused by the joint effects of different substances. Against this background, the application by Karriker-Jaffe and colleagues of simultaneous co-use as a measure in their article can be seen as a great advantage giving us valuable information.

Karriker-Jaffe and colleagues note that if only heavy alcohol use is screened for this may miss a sizeable proportion of those using alcohol and drugs simultaneously, since their alcohol use does not necessarily exceed the typical high-risk threshold. Although the authors highlight the importance of screening for alcohol and drugs, it could be expanded for the simultaneous use of different substances more generally. For example, in a Finnish population-based study illicit drug use has been shown to have increased notably during the 2000s among those using prescription drugs non-medically (Karjalainen, Lintonen, & Hakkarainen, 2017). Although in this Finnish study it could not be confirmed whether prescription drugs and illicit drugs were used simultaneously or not, for example benzodiazepines and opioids are reported to be widely co-abused in other studies (Jones, Mogali, & Comer, 2012). Thus, this population using illicit drugs and prescription drugs non-medically might also benefit if they were screened for simultaneous use and referred to treatment, if needed. This is all the more important since, according to the existing literature, many of those with prescription drug dependence or disorders do not utilise or receive substance-abuse treatment (McCabe, Cranford, & West, 2008).

In the Finnish social and healthcare services approximately one third of substance abusers seeking help have used two or more substances simultaneously during last year; the most common combinations being alcohol and prescription drugs and illicit drugs and prescription drugs (Kuussaari, Karjalainen, Kataja, & Hakkarainen, 2017). Since those using multiple drugs may encounter many different adversities such as social or health problems (Kuussaari et al., 2017) or even premature mortality (Gjersing & Bretteville-Jensen, 2018), they should be identified in the service system. This is important from the point of view of treatment, but also in preventing the accumulation of problems. However, when more emphasis is placed on identifying those in need for treatment, it is crucial for the service system to be able to respond to the possibly increasing demand.