Background: Like other complex psychosocial interventions, mindfulness-based treatments comprise various modality-specific components as well as nonspecific therapeutic ingredients that collectively contribute to efficacy. Consequently, the isolated effects of mindfulness strategies per se remain unclear.Methods: Using a randomized double-blind design, we compared the isolated effects of 11-minutes of "supervised" mindfulness instruction against a closely matched active control (relaxation) on subjective, physiological, and behavioral indices of maladaptive alcohol responding in drinkers at risk of harm from alcohol use (n = 68). Simple follow-up instructions on strategy use were provided, but practice was unsupervised and not formally monitored.Results: Both groups showed acute reductions in craving after training, although a trend group x time interaction (P = .056) suggested that this reduction was greater in the relaxation group (d = 0.722 P < .001) compared with the mindfulness group (d = 0.317, P = .004). Furthermore, upregulation of parasympathetic activity was found after relaxation (d = 0.562; P < .001) but not mindfulness instructions (d = 0.08; P > .1; group x time interaction: P = .009). By contrast, only the mindfulness group showed a reduction in past-week alcohol consumption at 7-day follow-up (-9.31 units, d = 0.593, P < .001), whereas no significant reduction was seen in the relaxation group (-3.00 units, d = 0.268, P > .1; group x time interaction: P = .026).Conclusion: Very brief mindfulness practice can significantly reduce alcohol consumption among at-risk drinkers, even with minimal encouragement to use this strategy outside of the experimental context. The effects on consumption may therefore represent a lower bound of efficacy of "ultra-brief" mindfulness instructions in hazardous drinkers, at least at short follow-up intervals.