This is one of the most under-discussed aspects of Mounjaro treatment, and it's important. If you take the oral contraceptive pill or oral HRT, Mounjaro may reduce how well these medications work.
Why does this happen?
Mounjaro slows gastric emptying — how quickly food and other substances leave your stomach and move into your small intestine. Oral medications, including contraceptive pills and oral HRT tablets, need to be absorbed through the gut to work. If gastric emptying is significantly delayed, absorption may be reduced or become less predictable, potentially lowering the medication's effectiveness.1
This effect has been observed specifically with tirzepatide (Mounjaro). While all GLP-1 medications slow gastric emptying, the MHRA has issued this warning for Mounjaro specifically. Wegovy and Saxenda do not currently carry the same warning, though the underlying mechanism is similar.1
What the MHRA recommends
The MHRA advises that if you take an oral contraceptive pill while using Mounjaro, you should use an additional non-oral method of contraception (such as condoms) in the following situations:1
- For 4 weeks after starting Mounjaro
- For 4 weeks after each dose increase
This is because the effect on gastric emptying is most pronounced when the medication is new or the dose changes. Once you've been on a stable dose for more than 4 weeks, the risk is considered lower — though the MHRA still advises awareness.
What about vomiting and diarrhoea?
If Mounjaro causes vomiting within 3 hours of taking your contraceptive pill, or causes severe diarrhoea lasting more than a day, you should follow the guidance for missed pills in your contraceptive's patient information leaflet. In these situations, your pill may not have been properly absorbed.2
Contraception methods NOT affected
Non-oral contraception methods are not affected by Mounjaro because they don't rely on gut absorption:
- Contraceptive implant (e.g. Nexplanon)
- Hormonal IUD/coil (e.g. Mirena)
- Copper IUD/coil
- Contraceptive injection (e.g. Depo-Provera)
- Contraceptive patch
- Vaginal ring
- Condoms
If you're starting Mounjaro and currently use the oral pill, it may be worth discussing with your GP whether switching to a non-oral method would be more convenient than using barrier contraception alongside the pill during dose changes.
Oral HRT is also affected
If you take oral hormone replacement therapy (HRT) — such as Utrogestan (progesterone) or oral oestrogen tablets — Mounjaro may also reduce its effectiveness. The progesterone component is particularly important as it protects the endometrium (womb lining). The MHRA recommends speaking to your GP about switching to non-oral HRT forms such as patches, gels, or the Mirena coil.1
If your HRT is already delivered via patches, gels, or a Mirena coil, you don't need to make any changes.
What about Wegovy and Saxenda?
At the time of writing, the MHRA has not issued the same contraception warning for Wegovy (semaglutide) or Saxenda (liraglutide). However, since all GLP-1 medications slow gastric emptying, the potential for interaction exists. If you have concerns, discuss with your prescriber. The Faculty of Sexual and Reproductive Healthcare (FSRH) has published guidance on GLP-1 medications and contraception that your GP can refer to.2