Inclusion Criteria:

1. Have a diagnosis of moderate-to-severe plaque PsO, as defined by a dermatologist or other experienced clinician treated PsO (for example, allergologist, nurse practitioner or physician assistant)
2. Have body mass index (BMI) of 30 kilograms per meter squared (kg/m²) or greater (obesity) or 27 kg/m² to <30 kg/m² (overweight) in the presence of at least 1 weight-related comorbid condition (hypertension, dyslipidemia, type 2 diabetes mellitus, obstructive sleep apnea, or cardiovascular diseases).
3. Must have initiated treatment with ixekizumab for approximately 3 months (± 1 month) prior to decision to add tirzepatide.
4. Must be able to initiate tirzepatide (Day 0) within 30 days of treatment decision (baseline/screening).

Exclusion Criteria:

1. Have currently received ixekizumab for more than 4 months or less than 2 months.
2. Have had any exposure to tirzepatide or other glucagon-like peptide-1 receptor agonist (GLP-1 RAs), for example, dulaglutide, liraglutide, or semaglutide.
3. Are currently enrolled in any other clinical study.

Other exclusions

1. Have a known hypersensitivity to tirzepatide or to any of its component.
2. Have a personal or family history of medullary thyroid cancer.
3. Have multiple endocrine neoplasia type 2.
4. Have type I diabetes mellitus.
5. Have a history of chronic or acute pancreatitis at any time before screening (Visit 1).
6. Have a history of proliferative diabetic retinopathy, diabetic maculopathy, or nonproliferative diabetic retinopathy that requires acute treatment.
7. Have a history of ketoacidosis or hyperosmolar state/coma.
8. Have a history of severe hypoglycemia and hypoglycemia unawareness within the 6 months before screening.
9. Have a history of severe gastrointestinal complications, including gastroparesis, gastroesophageal reflux disease, dyspepsia, chronic nausea/constipation/vomiting.