Introduction: High-drive working dogs often struggle to disengage or down-regulate arousal between tasks, creating operational challenges and welfare concerns. Fast-acting, non-sedative autonomic-modulating nootropics, formulations designed to transiently reduce arousal and promote behavioral calming, may offer a viable alternative to traditional sedatives or anxiolytics. Thus, this study examined the acute behavioral, cognitive, and task-engagement effects of a fast-acting autonomic-modulating nootropic in working dogs. Methods: Ten high-drive working dogs completed two test sessions: baseline (CTRL) and a day receiving a fast-acting autonomic-modulating nootropic (CALM®). Dogs performed (1) sustained-attention focus-hold trials at 30, 60, and 90 s with preferred and non-preferred stimuli; (2) puzzle-solving tasks (Levels 1–2); and (3) behavioral intensity ratings (1–5 scale). All duration-based outcomes were converted to percentage of maximal possible time. Within-dog differences between CTRL and CALM® were analyzed using paired t-tests with Cohen’s d_z effect sizes, and cap-hit frequencies were summarized descriptively. Results: CALM® significantly reduced sustained attention across all non-preferred durations (p = 0.023–0.038; dz = –0.77 to –0.87) and at the 90 s preferred interval (p = 0.004; dz = –1.22), with similar nonsignificant trends at 30–60 s (p ≥ 0.070; dz = –0.63 to –0.65). Puzzle-solving times showed small-to-moderate nonsignificant slowing (dz = –0.36 to –0.51), with more unsolved Level 2 puzzle items under CALM® (1 CTRL vs 4 CALM®). Dogs that encountered an impasse during CALM® testing frequently disengaged or sought handler cues. Behavioral intensity decreased across both focus-hold and puzzle tasks (dz = –0.24 to –0.80), consistent with reduced arousal. Conclusions: CALM® produced a coherent down-regulation of arousal and engagement intensity without impairing cognition, consistent with its autonomic-modulating formulation. These preliminary findings suggest utility for helping high-drive dogs disengage in overstimulating environments, and they support the need for larger controlled trials across diverse working-dog and handler populations.