The Mounjaro and Zepbound prescribing information includes a specific instruction: people using oral hormonal birth control should switch to a non-oral method, or add a barrier method, for 4 weeks after starting the peptide and for 4 weeks after each dose increase.

The mechanism is documented. A single 5 mg dose of tirzepatide reduces the peak concentration of ethinyl estradiol (the estrogen in most birth-control pills) by about 59%.

The semaglutide label describes delayed gastric emptying as a class property but doesn't carry the same explicit contraceptive instruction.

"GLP-1 medications affect birth control" collapses two different label situations into one. For tirzepatide, the 4-week barrier-method window is real and labeled. For semaglutide, the same instruction isn't on the label.