The main purpose of this study is to evaluate the response of glucagon to insulin-induced low blood sugar after administration of the study drug LY3532226 in participants with type 1 diabetes mellitus (T1DM). The study will also evaluate if LY3532226 helped participants to recover from insulin-induced low blood sugar condition compared to placebo. The study will last approximately 16 weeks excluding screening period.

Inclusion Criteria:

• Participants with type 1 diabetes mellitus (T1DM) for at least 2 years treated with insulin
• Body mass index (BMI) of 18.5 to 40.0 kilograms per meter squared (kg/m²)
• Are males or females not of childbearing potential

Exclusion Criteria:

• Have acute proliferative retinopathy requiring active treatment within 3 months of screening
• Have been treated with dipeptidyl peptidase-Ni, GLP-1 receptor agonists, GIP agonists, metformin or sodium-glucose cotransporter 2 inhibitors within the previous 3 months
• Have received systemic or inhaled glucocorticoid therapy
• Women of childbearing potential
• Are currently taking part in another clinical study trial involving medical research, or have participated within the last 30 days of screening in a clinical study involving a study intervention