Background Dog ownership is suggested to improve mental well-being, although empirical evidence among community dog owners is limited. This study examined changes in human mental well-being following dog acquisition, including four measures: loneliness, positive and negative affect, and psychological distress. Methods We conducted an eight-month controlled study involving three groups (n = 71): 17 acquired a dog within 1 month of baseline (dog acquisition); 29 delayed dog acquisition until study completion (lagged control); and 25 had no intentions of acquiring a dog (community control). All participants completed the UCLA Loneliness Scale (possible scores 0–60), Positive and Negative Affect Schedule and Kessler10 at baseline, three-months and eight-months. We used repeated measures ANCOVAs to analyse data with owner age and sex included as covariates. Post-hoc tests were performed for significant effects (p \u3c 0.05). Results There was a statistically significant group by time interaction for loneliness (p = 0.03), with an estimated reduction of 8.41 units (95% CI -16.57, − 0.26) from baseline to three-months and 7.12 (95% CI -12.55, − 1.69) from baseline to eight-months in the dog acquisition group. The group by time interaction for positive affect was also significant (p = 0.03), although there was no change in the dog acquisition group. Conclusions Companion dog acquisition may reduce loneliness among community dog owners. Our study provides useful direction for future larger trials on the effects of dog ownership on human mental well-being
