Switching from Mounjaro 2.5 mg to Zepbound 5 mg After 8 Weeks
No, a patient should not start Zepbound at 5 mg after being on Mounjaro 2.5 mg for 8 weeks—both medications contain the identical active ingredient (tirzepatide) at the same doses, so this represents continuing the same medication rather than switching, and the patient should follow standard dose escalation protocols by increasing to the next dose level (5 mg) after at least 4 weeks at 2.5 mg.
Understanding Mounjaro vs. Zepbound
Mounjaro and Zepbound are the same medication (tirzepatide) marketed under different brand names—Mounjaro is FDA-approved for type 2 diabetes while Zepbound is approved for chronic weight management, but both contain identical tirzepatide formulations at the same available doses (2.5 mg, 5 mg, 10 mg, and 15 mg) 1, 2.
The distinction between these brands is purely regulatory and marketing-based, not pharmacological, so "switching" from one to the other at the same or different dose is simply continuing tirzepatide therapy 3, 1.
Standard Tirzepatide Dose Escalation Protocol
Tirzepatide should be initiated at 2.5 mg once weekly subcutaneously, then increased to 5 mg after at least 4 weeks 1, 2.
After 8 weeks on the 2.5 mg dose, the patient has exceeded the minimum 4-week period required before dose escalation, making them eligible to increase to 5 mg 3, 1.
The dose can be further increased in 2.5 mg increments after at least 4 weeks at each dose level to achieve optimal glycemic control or weight loss, with maintenance doses of 5 mg, 10 mg, or 15 mg 4, 1.
Clinical Rationale for Dose Escalation Timing
The 4-week minimum at each dose level allows for assessment of tolerability, particularly gastrointestinal adverse events (nausea, diarrhea, vomiting) which are most common during dose escalation and typically mild to moderate in severity 1, 2.
Tirzepatide demonstrates dose-dependent efficacy, with higher doses (15 mg) achieving up to 20.9% weight reduction compared to 15% at lower doses in non-diabetic patients with obesity 4, 2.
After 8 weeks at 2.5 mg, patients should be evaluated for both tolerability and preliminary efficacy before advancing to the next dose 4, 5.
Practical Implementation
Simply continue the dose escalation by prescribing tirzepatide 5 mg once weekly (whether labeled as Mounjaro or Zepbound depending on the indication) after confirming adequate tolerability at the 2.5 mg dose 1, 2.
If the patient has experienced significant gastrointestinal adverse events at 2.5 mg that have not resolved, consider remaining at 2.5 mg for an additional 4 weeks before escalation 1, 2.
For weight loss indications, evaluate efficacy at 12-16 weeks from treatment initiation using the maximum tolerated dose reached, with a threshold of 4-5% body weight loss to determine whether to continue therapy 5.
The patient should remain on each dose level for at least 4 weeks before further escalation to 10 mg or 15 mg if additional weight loss or glycemic improvement is needed 4, 1.