The effect of forming implementation intentions on alcohol consumption: A systematic review and meta-analysis

Issues
Meta-analysis was used to estimate the effect of forming implementation intentions (i.e., if-then plans) on weekly alcohol consumption and heavy episodic drinking (HED). Sample type, mode of delivery, intervention format and timeframe were tested as moderator variables.

Approach
Cochrane, EThOS, Google Scholar, PsychArticles, PubMed and Web of Science were searched for relevant publications to 31 March 2021. Random-effects meta-analysis was used to estimate the effect size difference (d) between individuals forming versus not forming implementation intentions on weekly consumption and HED.

Key Findings
Sixteen studies were included in meta-analyses. The effect size difference for forming implementation intentions on weekly alcohol consumption was d+ = −0.14 confidence interval (CI) [−0.24; −0.03]. Moderator analyses highlighted stronger effects for: (i) community (d+ = −0.38, CI [−0.58; −0.18]) versus university (d+ = −0.04, CI [−0.13; 0.05]) samples; (ii) paper (d+ = −0.26, CI [−0.43; −0.09]) versus online (d+ = −0.04, CI [−0.14; 0.06]) mode of delivery; and (iii) volitional help sheet (d+ = −0.34, CI [−0.60; −0.07]) versus implementation intention format (d+ = −0.07, CI [−0.16; 0.02]). In addition, effects diminished over time (B = 0.02, SE = 0.01, CI [0.03; 0.01]). Forming implementation intentions had a null effect on HED, d+ = −0.01 CI [−0.10; 0.08].

Implications
Forming implementation intentions reduces weekly consumption but has no effect on HED.

Conclusion
This review identifies boundary conditions on the effectiveness of implementation intentions to reduce alcohol consumption. Future research should focus on increasing the effectiveness of online-delivered interventions and integrating implementation intention and motivational interventions.