Wegovy vs Mounjaro when you use oral contraception (COC or POP)

If you use oral contraception, either the combined pill (COC) or the progestogen-only pill (POP), and start a GLP-1 injection, the key concern is whether your contraception stays reliable. This matters most during dose increases and if you experience vomiting or diarrhoea.

This comparison focuses only on Wegovy (semaglutide) and Mounjaro (tirzepatide), using UK-aligned evidence and guidance.

Key takeaways

  • Mounjaro (tirzepatide): if you use oral contraception (COC or POP), switch to a non-oral method or add condoms for 4 weeks after starting and for 4 weeks after each dose increase.
  • Wegovy (semaglutide): product information indicates semaglutide is not anticipated to reduce oral contraceptive effectiveness, based on pharmacokinetic data with a combined pill.
  • For both medicines: vomiting or severe diarrhoea can make any oral contraceptive unreliable. Follow illness and missed pill rules and use condoms until protection is restored.
  • GLP-1 medicines should not be used in pregnancy. Use effective contraception and seek medical advice promptly if pregnancy occurs.

Why oral contraception is the focus

GLP-1 medicines can slow gastric emptying and commonly cause nausea, vomiting, or diarrhoea. That matters most for medicines taken by mouth, including COC and POP, because illness or delayed absorption can reduce reliability.

Non-oral contraception (for example, the implant, IUD or IUS, injection, patch, or ring) does not rely on stomach absorption in the same way. UK sexual health guidance indicates no extra precautions are needed with non-oral methods purely because of GLP-1 use. Suitability still depends on your medical history.

Wegovy vs Mounjaro: contraception impact comparison

Wegovy (semaglutide)

Wegovy product information states that semaglutide is not anticipated to decrease the effectiveness of oral contraceptives. This is based on data showing no clinically relevant change in overall exposure to hormones from a studied combined pill.

What this means in practice:

  • There is no specific instruction to use condoms for 4 weeks after each dose increase, unlike tirzepatide.
  • You still need a plan for vomiting or diarrhoea, because illness can reduce absorption of any oral pill.

Mounjaro (tirzepatide)

UK-aligned guidance states tirzepatide is the GLP-1 option with specific advice that it can reduce the effectiveness of oral contraception during initiation and dose increases. If you use oral contraception, COC or POP, you should either:

  • switch to a non-oral contraceptive method, or
  • add a barrier method such as condoms

Use extra precautions for 4 weeks after starting tirzepatide and for 4 weeks after each dose increase.

Practical planning tip:

  • Tirzepatide is usually titrated in steps. This can mean repeated 4-week periods of extra protection during titration.

"The key difference is that Mounjaro has specific UK guidance for extra precautions with all oral contraception during initiation and dose increases, while Wegovy does not."

"If vomiting or diarrhoea is frequent, a non-oral contraceptive can be more reliable than repeatedly applying missed pill rules." Sorin Romaniuc, Pharmacist at Medino

What to do if you vomit or have diarrhoea (COC or POP)

Even if a GLP-1 does not meaningfully change contraceptive hormone exposure, vomiting or severe diarrhoea can still reduce absorption of oral pills.

Safety first approach:

  • If you vomit soon after taking your pill, treat this as a missed dose. Follow your pill leaflet instructions and use condoms until protection is restored.
  • If you have severe diarrhoea, apply the same approach as missed pills, based on NHS or sexual health guidance.
  • If these symptoms happen repeatedly on GLP-1 treatment, consider switching to non oral contraception and speak to a pharmacist or prescriber.

Switching from Wegovy to Mounjaro

UK sexual health guidance advises that if you switch from another GLP-1 treatment to tirzepatide, you should use a barrier method for 4 weeks after the switch, and again for 4 weeks after any dose increase, if you use oral contraception.

Pregnancy and breastfeeding

UK safety communications advise that GLP-1 medicines should not be used in pregnancy due to limited human safety data. Effective contraception should be used while taking them. If pregnancy occurs, contact your prescriber promptly for advice.

When to seek urgent help

Seek urgent medical help if you have:

  • signs of a severe allergic reaction, such as swelling of the face, lips or tongue, or breathing difficulty
  • persistent vomiting with inability to keep fluids down, especially with signs of dehydration
  • severe or worsening abdominal pain that does not settle

If you are worried but it is not an emergency, contact NHS 111 or your prescriber.

FAQ

Does Mounjaro affect the combined pill only, or all oral contraceptives?

The extra precautions apply to all oral contraceptives, including the combined pill (COC) and the progestogen-only pill (POP). Use condoms or switch to a non-oral method for 4 weeks after starting and 4 weeks after each dose increase.

Does Wegovy affect the POP too?

Wegovy product information states that semaglutide is not anticipated to reduce the effectiveness of oral contraceptives, based on data with a combined pill. Vomiting and diarrhoea can still make any oral pill unreliable.

Do I need condoms after every Wegovy dose increase?

There is no specific Wegovy instruction to use condoms after each dose increase. The main practical risk is illness affecting absorption.

What if I am switching from Wegovy to Mounjaro?

If you use oral contraception and switch to Mounjaro, use condoms or switch to a non-oral method for 4 weeks after switching. Repeat this for 4 weeks after each dose increase.

If I am vomiting on either injection, what is the safest contraception approach?

If vomiting or diarrhoea is frequent, a non-oral contraceptive is often the most reliable way to avoid absorption problems. Discuss options with a clinician.

Does this apply to emergency contraception tablets?

Evidence is limited. If you need emergency contraception while taking a GLP-1 medicine, seek urgent advice from a pharmacist or sexual health service. A non-oral emergency contraception option may be considered depending on timing and circumstances.

When to speak to a pharmacist or GP

Speak to a pharmacist or GP if:

  • you use COC or POP and are starting Mounjaro, increasing the dose, or switching onto it
  • you have vomiting or diarrhoea and are unsure how long to use condoms or how to apply missed pill rules
  • you are planning pregnancy or think you may be pregnant while using a GLP-1 medicine
  • you have severe side effects, dehydration, severe abdominal pain, or any red flag symptoms

References

UK product information (SmPC and EPAR)

UK contraception and interaction guidance

NHS guidance on pill illness and missed pills

Regulatory safety communication

Peer reviewed evidence (semaglutide and combined pill pharmacokinetics)

Written by Alessandro Grenci
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