The review conducted by Staiger and colleagues  draws attention to a commonly observed problem among addiction treatment clients: alcohol use that impedes recovery from drug use. One of the main conclusions from the review is that the role of alcohol use in drug recovery is woefully understudied. Importantly, this problem has been described in the literature for 10 years , yet only 13 of 576 peer-reviewed papers met the key inclusion criteria of being a drug treatment study that reported alcohol use before treatment, at the end of treatment and at some point following treatment. Correspondingly, there is little research on the role of drug use in recovery from an alcohol use disorder, even though the data suggest that drug dependence predicts alcohol dependence recovery significantly . Furthermore, models of alcohol and drug relapse have generally not included other contemporaneous substance use as a risk factor in the relapse process [4-7]. The results from the Staiger et al.  review, which provided support for the hypothesis that alcohol use increases the risk of relapse to drug use, would suggest that this is a serious omission.
In my view, three questions need to be addressed in order to move the research forward and help clients in recovery from alcohol and drug use disorders. First, the authors distinguished alcohol use from the ‘primary addiction’ repeatedly throughout the review. As noted in the review, many treatment programs assume that principles of treatment will be effective for the primary addiction and other drugs of abuse, such that treating alcohol use explicitly is not necessary. It was also noted that addiction treatment programs may be wary of treating all substances, because ‘depriving clients of all substances’ may be too harsh and potentially reduce motivation for treatment of the primary addiction. Based on these examples, it is unclear to what extent thinking about alcohol or drug use as primary or secondary is necessarily a helpful approach in the treatment of addiction. Could programs be developed that address the common predictors of relapse across all drugs of abuse (e.g. issues with craving, negative affect, social pressure, etc.) with less regard to treating a specific primary addiction?
The second question concerns whether or not the level of measurement in the studies reviewed by Staiger et al.  was sufficient to answer the questions posed in the review. It was noted that relapses to other substances often co-occurred with relapse to alcohol use (e.g. ), but the question of whether alcohol use triggers drug relapse, drug relapse triggers alcohol use or whether they simply happen to co-occur is still unanswered. Research that examines the temporal sequencing of individual differences in moment-to-moment alcohol and drug use following treatment will be necessary to address this question sufficiently. For example, using ecological momentary assessment  in a non-treatment-seeking group of college students, our prior research has found that on the majority of occasions (54.9%) the students started drinking before they started smoking . This level of measurement will be helpful for answering the question of whether alcohol use increases the risk of drug relapse.
The final question asks whether or not clinicians and researchers should be conceptualizing alcohol use as a ‘risk factor’ for relapse or as a part of the larger complex process of relapse. I would argue that contemporaneous substance use during recovery from a ‘primary addiction’ probably occurs within the context of a high-risk situation and that the same combinations of risk factors may equally influence the use of alcohol, as well as relapse to drug use . This conceptualization also places alcohol use within the broader spectrum of common risk factors that could be targeted in a more generic addiction treatment approach. In a high-risk situation a client is not likely to consider whether alcohol use will put them at risk for relapse to their primary addiction; rather, they are probably searching for any method of escaping, avoiding or managing the interpersonal or intrapersonal factors that are happening in that moment. In that situation, a client needs broader skills for recognizing those factors and coping with whatever is happening without reaching for a substance, regardless of whether that substance is alcohol or their ‘primary drug’.
Declaration of interests