Abstract Background Phenylbutazone is often prescribed to manage pain caused by hyperinsulinemia‐associated laminitis, but in diabetic people nonsteroidal anti‐inflammatory drugs increase insulin secretion and pancreatic activity. Hypothesis/Objectives Investigate the effect of phenylbutazone administration on insulin secretion in horses. It was hypothesized that phenylbutazone will increase insulin secretion in horses with insulin dysregulation (ID). Animals Sixteen light breed horses, including 7 with ID. Methods Randomized cross‐over study design. Horses underwent an oral glucose test (OGT) after 9 days of treatment with phenylbutazone (4.4 mg/kg IV q24h) or placebo (5 mL 0.9% saline). After a 10‐day washout period, horses received the alternative treatment, and a second OGT was performed. Insulin and glucose responses were compared between groups (ID or controls) and treatments using paired t test and analyses of variance with P < .05 considered significant. Results In horses with ID, phenylbutazone treatment significantly decreased glucose concentration ( P = .02), glucose area under the curve (2429 ± 501.5 vs 2847 ± 486.1 mmol/L × min, P = .02), insulin concentration ( P = .03) and insulin area under the curve (17 710 ± 6676 vs 22 930 ± 8788 μIU/mL × min, P = .03) in response to an OGT. No significant effect was detected in control horses. Conclusion and Clinical Importance Phenylbutazone administration in horses with ID decreases glucose and insulin concentrations in response to an OGT warranting further investigation of a therapeutic potential of phenylbutazone in the management of hyperinsulinemia‐associated laminitis beyond analgesia.