Short answer: FDA labels say not to combine: tirzepatide shouldn't be used with any GLP-1 drug like semaglutide.
Both drugs act on the GLP-1 receptor. The Wegovy label says use with any other GLP-1 receptor agonist is not recommended, and the Zepbound label says the same about tirzepatide with any GLP-1 receptor agonist. Combining them has not been studied.
Each label separately lists gastrointestinal side effects, sometimes severe, and a warning about acute pancreatitis. Both drugs slow stomach emptying, which can affect oral medicines; the Zepbound label also advises people on oral birth control to switch to a non-oral method or add a barrier method for 4 weeks after starting and after each dose increase. Both lower blood sugar, and the risk of low blood sugar rises when used with insulin or sulfonylureas.
FDA label. The interaction is described in the FDA-approved prescribing information for at least one of the two. Avoid: An FDA label or strong evidence says not to combine these, or they duplicate the same treatment.
Guides: Semaglutide, Tirzepatide. To check this pair alongside others, open it in the peptide interaction checker.