Why the pill may work less well
Tirzepatide slows gastric emptying. As a result, the pill may be absorbed later and in smaller amounts. The prescribing information therefore recommends using additional contraception at the start and for four weeks after each dose increase, or switching to a non-oral method (e.g. IUD/coil, ring, patch). For semaglutide, studies found no relevant effect on the pill – talk to your doctor anyway.
In addition, this applies to everyone: if you vomit or have severe diarrhoea after an injection, treat the pill as unreliable, just as you would with any stomach bug.
Unplanned pregnancies
There are many reports of unplanned pregnancies on GLP-1 medications. One reason: in women with overweight or PCOS (polycystic ovary syndrome), weight loss can restart ovulation – fertility goes up. If you don’t want to get pregnant, you should therefore review your contraception deliberately.
The medications are not approved during pregnancy and breastfeeding. If you are planning a pregnancy, the prescribing information recommends stopping in good time beforehand – discuss how long beforehand with your doctor.
PCOS and the weight-loss injection
With PCOS, insulin resistance and overweight often play a big role. GLP-1 medications are being studied in PCOS and can improve weight and metabolism – but they are not approved for PCOS itself. Treatment belongs in the hands of a gynaecologist or endocrinologist, not least because of the contraception question.
And with unapproved substances?
For retatrutide, cagrilintide or research tirzepatide there is no prescribing information and no verified data on interactions with the pill. Because they also slow gastric emptying, you should assume at least the same risk.
When to see a doctor
- You take the pill and are starting a GLP-1 medication or increasing the dose
- You want to have a baby or could be pregnant
- Your period is late or missing
In an emergency: 112.
FAQ
Does the pill still work with Mounjaro?
It may work less well, especially at the start and after dose increases. The prescribing information then recommends an additional barrier method or non-oral contraception for four weeks.
Does Ozempic affect the pill?
Studies found no relevant effect for semaglutide. With vomiting or severe diarrhoea, however, the pill should always be considered unreliable.
Does the weight-loss injection make you more fertile?
Weight loss can improve ovulation in people with overweight or PCOS. Many report unplanned pregnancies – so review your contraception deliberately.
Sources
This article does not replace medical advice. It gives no dosing recommendations. As of September 2026.