The main purpose of this study was to look if the study drug, tirzepatide, gets into the breastmilk and, if yes, how long it takes the body to get rid of it from the breastmilk. The study drug was given as a single injection under the skin in healthy lactating females. For each participant, the total duration of the study was approximately 8 weeks, including screening.

Inclusion Criteria:

• Participants who are overtly healthy females as determined by medical evaluation
• Female participants who delivered normal-term infant (at least 37 weeks gestation) and are at least 6 weeks postpartum at the time of screening
• Body mass index (BMI) between 18.5 and 40.0 kilograms per meter squared (kg/m²), inclusive
• Female participants who has well-established lactation and is breastfeeding her infant. Note: Breastfeeding must be discontinued prior to the administration of tirzepatide on Day 1 and not resumed for the remaining duration of the study until a follow-up visit (or for total of 29 days after tirzepatide dosing for participants who discontinue early).

Exclusion Criteria:

• Have a history of inadequate lactation (for multiparous females who have previously breastfed)
• Have confirmed type 1 or type 2 diabetes mellitus
• Regularly use known drugs of abuse or show positive findings on drug screen

All enrolled participants.

Baseline to the end of follow-up (up to Day 29)

All enrolled participants who received a dose of Tirzepatide.