As millions turned to GLP-1 medications for weight loss, digestive discomfort affected 58% of users. Haleon wanted to help using its portfolio, from TUMS to Benefiber to Gas-X, before they gave up. But GLP-1 users were a fast-growing, poorly understood audience with no playbook. So Digitas and Haleon built three Gen-AI agents to think and respond like current, lapsed, and prospective users, trained on health claims data and 7,000+ behavioral signals. Through real-time chatbot interactions, these living personas tested claims, ranked creative, and weighed in on displays, fueling hyperpersonalized creative and media across programmatic, social, influencer, and a dedicated Amazon storefront.