With an increasing prevalence of obesity, there is a need for new therapies to improve body weight management and metabolic health. Multireceptor agonists in development may provide approaches to fulfill this unmet medical need. LY3437943 is a novel triple agonist peptide at the glucagon receptor (GCGR), glucose-dependent insulinotropic polypeptide receptor (GIPR), and glucagon-like peptide-1 receptor (GLP-1R). In vitro, LY3437943 shows balanced GCGR and GLP-1R activity but more GIPR activity. In obese mice, administration of LY3437943 decreased body weight and improved glycemic control. Body weight loss was augmented by the addition of GCGR-mediated increases in energy expenditure to GIPR- and GLP-1R-driven calorie intake reduction. In a phase 1 single ascending dose study, LY3437943 showed a safety and tolerability profile similar to other incretins. Its pharmacokinetic profile supported once-weekly dosing, and a reduction in body weight persisted up to day 43 after a single dose. These findings warrant further clinical assessment of LY3437943. Display omitted •LY3437943 has triple agonist activity at the glucagon, GIP, and GLP-1 receptors•LY3437943 caused greater body weight loss in obese mice than tirzepatide•LY3437943 increased energy expenditure through glucagon receptor activation•Safety and tolerability of LY3437943 were similar to other incretin-based drugs Coskun et al. demonstrate that LY3437943, a triple glucagon, GIP, and GLP-1 receptor agonist for the treatment of obesity and type 2 diabetes, can reduce body weight through increased energy expenditure and reduced calorie intake in obese mice. Its safety and tolerability in healthy participants were similar to other incretin-based therapies.