Tirzepatide is an investigational medication that has been studied for the treatment of diabetes when administered once a week by self-injection. In these trials people who received the medication also lost some weight. This study is being done to see how safe tirzepatide is and how well it will work to help people who are obese or overweight to lose weight, when it is used along with a reduced-calorie diet and increased physical activity.

Participants will be randomly assigned to one of three doses of tirzepatide or to a placebo (inactive look-alike drug). They will be followed for either 72 or 176 weeks depending on the results of an initial test of blood sugar control.