Weight Loss With Microdose Tirzepatide: Real-World Outcomes in Patients Initiating Treatment Below 2.5 mg Weekly

Background: Tirzepatide is conventionally initiated at 2.5 mg weekly and titrated to approved maintenance doses. Evidence describing weight change at injectable starting doses below 2.5 mg/week is limited. Methods: We conducted a retrospective, single-organization observational study of adults documented as new GLP-1 starts, with baseline body mass index (BMI) [≥]27 kg/m2, who initiated compounded injectable tirzepatide at a microdose of 1 or 2 mg/week (below the standard 2.5 mg/week starting dose). Source records were reviewed for baseline validity, prior treatment, weight consistency, and treatment exposure. The main descriptive analysis selected the latest eligible measurement per patient within observation windows of 14-35, 36-59, and 60-89 days of adjudicated treatment exposure, excluding observations after escalation above 2 mg/week. All 93 eligible measurements were included in a supporting random-intercept model. Analyses were retrospective and hypothesis-generating; no formal sample-size calculation was performed. Results: Sixty patients contributed 93 eligible follow-up measurements, of which 84 were selected for patient-window summaries. Mean age was 47.3 years, 81.7% were female, and mean baseline BMI was 33.3 kg/m2. Mean body-weight loss was 2.18% (95% CI 1.61-2.76; n=57) in the 14-35-day window at a median 21 days, 3.58% (95% CI 2.43-4.72; n=19) in the 36-59-day window at a median 48 days, and 6.10% (95% CI 4.60-7.60; n=8) in the 60-89-day window at a median 65.5 days. The adjusted model estimated 2.16 percentage points greater loss per 30 days of treatment exposure (95% CI 1.69-2.63). Conclusions: Weight loss was observed within the 14-35-, 36-59-, and 60-89-day observation windows among evaluable adults initiating compounded injectable tirzepatide at 1-2 mg/week. These uncontrolled findings are hypothesis-generating; the 36-59- and 60-89-day estimates are particularly limited by sparse follow-up.