TIRZEPATIDE: WHAT THE LABEL SAYS
The Mounjaro and Zepbound prescribing information gives a specific label instruction for people using oral hormonal birth control: a non-oral method, or an added barrier method, is named for 4 weeks after starting tirzepatide and for 4 weeks after each dose increase. That is a prescriber conversation, not a general GLP-1 rule.
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%.
SEMAGLUTIDE: WHAT THE LABEL DOESN'T SAY
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.
What this means
This one is specific to the peptide, not the class.
The label for tirzepatide names the window. The label for semaglutide doesn't.