BACKGROUND AND AIMS: Problem gambling and unhealthy alcohol use often co-occur. The current trial sought to establish whether adding a brief online intervention for unhealthy alcohol use to an online problem gambling intervention would lead to improvements in gambling and drinking among those with both of these concerns. METHODS: Participants were recruited from across Canada using an advertisement targeting those concerned about their gambling who were interested in online help. No mention of unhealthy alcohol use was made in the advertisement. Participants meeting criteria for problem gambling were randomized to either receive just an online intervention for gambling (G-only) or to receive an online gambling intervention plus a brief personalized feedback intervention for unhealthy alcohol use (G + A). Participants were followed up at 3 and 6 months. RESULTS: A total of 282 participants were recruited for the trial. Follow-up rates were good (80% and 84% at 3 and 6 months). There were significant reductions in gambling (p < .001) across time but no significant differences (p > .05) between those who received either the G-only or G + A interventions. Further, for those with unhealthy alcohol use (41% of the sample), there were no significant reductions in alcohol consumption (p > .05) across time or differences between condition. DISCUSSION AND CONCLUSION: The addition of a brief intervention for unhealthy alcohol use to an online intervention for gambling did not appear to improve either gambling or drinking outcomes among people concerned about their gambling. Further research is merited to examine whether a combined intervention (with gambling and drinking components integrated) might result in improved outcomes and whether such an intervention might benefit the subgroup of participants who would specifically seek help for both gambling and alcohol concerns.ClinicalTrials.govNCT03323606; Registration date: October 24, 2017.