Evidence-graded answer
Does GLP-1 affect oral birth control?
Tirzepatide (Mounjaro, Zepbound) has documented reduced absorption of oral contraceptives during the first 4 weeks of each dose increase. Use backup contraception for ~4 weeks after starting + after each step-up. Semaglutide has no documented effect.
The FDA label for tirzepatide includes a warning that delayed gastric emptying reduces oral contraceptive absorption. The recommendation: barrier method for 4 weeks after initiation and 4 weeks after each dose escalation, or switch to a non-oral method (IUD, implant, injection, patch).
Semaglutide (Wegovy, Ozempic) labels do not include this warning — pharmacokinetic studies showed minimal effect on combined oral contraceptive levels.
For unplanned pregnancy risk reduction, IUD or implant is the strongest GLP-1-compatible option.
Source: Mounjaro prescribing information, accessdata.fda.gov