Semaglutide and tirzepatide have different pill rules

The well-known advice to add barrier contraception for four weeks after starting and after each dose increase applies to tirzepatide, the active ingredient in Mounjaro. Do not treat it as a rule for every GLP-1 medicine.

For semaglutide, interaction evidence shows no clinically relevant drop in levels of the oral contraceptives studied. You still need contraception. That evidence also does not cover the practical problems caused by vomiting, severe diarrhoea or missed pills.

What to do when you are sick

If you vomit soon after taking a contraceptive pill, or have severe or lasting diarrhoea, follow the illness and missed-pill instructions for your exact pill. Combined pills and progestogen-only pills have different rules. Ask a pharmacist or sexual health service if the instructions do not match what happened.

Depending on your pill type, the timing and recent sex, you may need extra contraception or advice about emergency contraception. Get advice promptly. Emergency options are time-sensitive, so do not wait for your next Wegovy consultation.

Non-oral contraception

An implant, intrauterine method, injection, patch or vaginal ring avoids the problem of a pill lost through vomiting or poorly absorbed during diarrhoea. Whether one suits you depends on your preferences and medical history. Not every method is right for every person.

If you change method, ask when the new one starts to work and how to stay covered in between. Stopping your pill the moment a replacement is booked leaves you exposed. Plan the change ahead of time. Reacting after repeated sickness is less safe.

Fertility and pregnancy assumptions

Weight loss and better metabolic health may change your cycle or the chance of ovulation in some people. Wegovy is not a licensed fertility treatment. Irregular periods or past trouble conceiving do not reliably prevent pregnancy. Do not rely on low fertility as your contraception.

If you miss a period or might be pregnant, follow pregnancy-testing advice and contact a clinician when needed. Do not assume nausea or breast symptoms come from the medicine. If you are pregnant, stop semaglutide and get prompt advice.

Planning pregnancy or switching GLP-1 medicines

Stop semaglutide at least two months before you try to conceive, and keep using contraception through the washout. Agree the end date with your prescriber. Do not work it out from a last injection date you are unsure of.

If you switch from Wegovy to Mounjaro, the tirzepatide-specific oral contraception precautions start to apply. If you switch the other way, confirm the changeover with your clinician. Do not assume the risk period ends the day you change. Keep one written plan naming the medicine, your contraception method, the main dates and where to get urgent advice if illness or missed pills disrupt it.

Sources

Your own medicine leaflet and prescriber come first. A source from another country does not mean the same rule applies in the UK.

  1. Wegovy FlexTouch UK prescribing information medicines.org.uk
  2. MHRA: GLP-1 medicines, what you need to know gov.uk
  3. FSRH: GLP-1 agonists and contraception fsrh.org

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