Does Mounjaro affect the pill? Can you get pregnant on Wegovy? UK guidance on contraception, fertility, pregnancy planning and breastfeeding on weight loss injections.
Do weight loss injections affect contraception and pregnancy?
Yes. If you could become pregnant, weight loss injections have important implications for contraception, pregnancy planning and breastfeeding.
In June 2025, the UK medicines regulator, the Medicines and Healthcare products Regulatory Agency (MHRA), issued guidance reminding women taking GLP-1 weight loss medicines of several key points:
- Weight loss injections should not be used during pregnancy, while trying to become pregnant, or while breastfeeding.
- Women who could become pregnant should use effective contraception during treatment.
- Mounjaro (tirzepatide) may reduce the effectiveness of the oral contraceptive pill in people who are overweight or obese.
- These medicines should be stopped for a period of time before trying to conceive.
This guide explains what the guidance means in practice, including which contraception to use, how long to stop treatment before trying for a baby, what to do if you become pregnant unexpectedly, and why weight loss can affect fertility.
Why shouldn't weight loss injections be used in pregnancy?
There is not enough evidence to show that Mounjaro, Wegovy or other GLP-1-based weight loss medicines are safe during pregnancy.
Studies in animals have shown potential harmful effects on the developing baby. There are not enough good-quality human studies to rule out risk.
There is also a more general reason.
Intentional weight loss is not recommended during pregnancy. Pregnancy is a time when your body needs adequate nutrition and energy to support your baby's growth. Medicines that substantially reduce appetite and food intake are not appropriate during this time.
For these reasons, the product information for Mounjaro and Wegovy advises that they should not be used during pregnancy.
Mounjaro and the contraceptive pill
This is one of the most important points for women taking Mounjaro.
The MHRA has highlighted that tirzepatide (Mounjaro) may reduce the effectiveness of oral contraceptives in people who are overweight or obese.
Why might Mounjaro affect the pill?
Mounjaro slows the rate at which your stomach empties.
This can affect how quickly and how completely medicines taken by mouth are absorbed. For the contraceptive pill, reduced absorption could mean lower hormone levels and less reliable protection against pregnancy.
This effect appears to be most significant when you first start treatment and after each dose increase.
What does the MHRA advise?
If you take an oral contraceptive pill (the combined pill or the progestogen-only pill) and are using Mounjaro, the MHRA advises:
Switch to a non-oral method of contraception, or add a barrier method such as condoms, for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase.
Mounjaro doses are usually increased in steps, often every four weeks, until you reach your maintenance dose. This means that, in practice, you may need extra contraceptive precautions for several months at the start of treatment.
Many women find it simpler to use a non-oral method throughout treatment.
Wegovy and the contraceptive pill
The MHRA's specific warning about reduced effectiveness of the pill applies to tirzepatide (Mounjaro).
Wegovy (semaglutide) is not currently considered to reduce the effectiveness of oral contraceptives in the same way.
However, all women who could become pregnant should use effective contraception while taking any GLP-1 weight loss medicine, including Wegovy.
Vomiting, diarrhoea and the pill
Whichever weight loss medicine you take, remember the standard rule for the contraceptive pill:
Severe vomiting or diarrhoea can stop the pill from being absorbed properly.
Nausea, vomiting and diarrhoea are common side effects of weight loss injections, particularly when starting treatment or increasing the dose.
If you vomit within a few hours of taking your pill, or have severe diarrhoea, you may not be protected. Follow the missed-pill advice in your pill's patient information leaflet, or ask a pharmacist, and use extra precautions such as condoms as advised.
For more on common side effects, read our guide to weight loss injection side effects.
Which contraception is best while taking weight loss injections?
Methods that do not rely on absorption from the stomach are not affected by changes in stomach emptying.
These include:
- The contraceptive implant (a small rod placed under the skin of the arm)
- The hormonal coil (intrauterine system or IUS)
- The copper coil (intrauterine device or IUD)
- The contraceptive injection
- The contraceptive patch
- The vaginal ring
- Condoms and other barrier methods, often used alongside another method
The implant and coils are known as long-acting reversible contraception (LARC). They are among the most effective methods available and do not depend on remembering to take a pill.
The best method for you depends on your medical history, preferences and plans for future pregnancy. Your GP, a sexual health clinic or a pharmacist can help you choose.
Please do not stop your current contraception without arranging an alternative.
Can weight loss injections make you more fertile?
This is one of the most talked-about topics online, often under headlines about "Ozempic babies" or "Mounjaro babies".
Some women taking weight loss injections have reported unexpected pregnancies, including women who believed they had difficulty conceiving.
There are several possible explanations:
- Weight loss can improve fertility. Excess weight is associated with irregular periods and reduced ovulation. Losing weight can help restore regular ovulation.
- Polycystic ovary syndrome (PCOS) is closely linked to excess weight and insulin resistance. Weight loss may improve cycle regularity and ovulation in women with PCOS.
- Reduced effectiveness of the oral contraceptive pill, particularly with Mounjaro, as described above.
- Vomiting and diarrhoea reducing absorption of the pill.
The practical message is important:
Do not assume you cannot get pregnant during treatment, even if you have had difficulty conceiving in the past.
Weight loss injections and PCOS
PCOS is a common hormonal condition that can cause irregular periods, excess hair growth, acne and difficulty conceiving. It is often associated with insulin resistance and excess weight.
Some women with PCOS find that weight loss on a GLP-1 medicine improves their symptoms and cycle regularity.
However, weight loss injections are licensed for weight management, not specifically for PCOS or infertility.
If you have PCOS and are planning a pregnancy, speak to your GP or specialist about the best approach. Weight loss before pregnancy may be beneficial, but the medicine must be stopped in good time before trying to conceive.
How long should you stop weight loss injections before trying to get pregnant?
The MHRA advises that GLP-1 weight loss medicines should be stopped before trying to become pregnant, to allow time for the medicine to leave your body.
The recommended wash-out periods are:
- Wegovy (semaglutide): stop at least 2 months before trying to conceive
- Mounjaro (tirzepatide): stop at least 1 month before trying to conceive
Semaglutide requires a longer gap because it stays in the body for longer.
If you are taking Wegovy tablets (oral semaglutide), the same semaglutide advice applies. If you are taking a newer medicine such as Foundayo (orforglipron), check the patient information leaflet and ask your prescriber for specific advice. You can read more in our guide to Foundayo in the UK.
Planning ahead
If you are thinking about pregnancy in the next year or so, it is worth discussing this with your prescriber early.
Things to consider include:
- When to stop treatment
- What support you will need to maintain your weight after stopping
- Starting folic acid before trying to conceive, as recommended for all women planning pregnancy
- Whether you need a higher dose of folic acid, which is often recommended for women with a BMI of 30 or more (your GP can advise)
- Any other medical conditions that need review before pregnancy
It is also important to know that appetite and weight often increase after stopping weight loss injections. Our article on what happens when you stop Mounjaro or Wegovy explains what to expect and how to prepare.
What if you become pregnant while taking weight loss injections?
If you find out you are pregnant while using Mounjaro, Wegovy or another GLP-1 medicine:
1. Stop taking the medicine. Do not take any further doses.
2. Contact your GP or midwife and let them know which medicine you were taking, the dose and when you took your last dose.
3. Let your prescriber know. At SynovaMed, you can contact our team and we will pause your treatment and support you.
4. Try not to panic. Early observational studies have not shown a clear increase in major birth defects in babies exposed to these medicines in early pregnancy, although the evidence is still limited. Your healthcare team can advise on any monitoring that may be appropriate.
5. Start folic acid if you are not already taking it, and follow the usual advice for early pregnancy.
The MHRA encourages suspected side effects, including those involving pregnancy, to be reported through the Yellow Card scheme. Your healthcare professional can help with this.
Can you take weight loss injections while breastfeeding?
No. Weight loss injections are not recommended while breastfeeding.
It is not known whether tirzepatide or semaglutide pass into breast milk in significant amounts, or what effect they might have on a baby.
Breastfeeding also increases your nutritional needs. A medicine that significantly reduces appetite may make it harder to eat enough to support both you and your baby.
If you would like to lose weight after having a baby, speak to your GP or health visitor about safe options while breastfeeding. Once you have stopped breastfeeding, weight loss injections may be considered if you meet the eligibility criteria.
Can you start weight loss injections after having a baby?
Many women find that weight gained during pregnancy is hard to lose.
If you are not breastfeeding and meet the eligibility criteria, you may be able to start treatment after pregnancy. Your prescriber will consider:
- How long ago you gave birth
- Whether you are breastfeeding
- Your current contraception
- Your physical and mental wellbeing
- Your BMI and medical history
You will need reliable contraception during treatment. If you are using the pill and considering Mounjaro, the same advice about extra precautions applies.
To check whether you may be eligible, see our guide: Am I eligible for weight loss injections in the UK?
Does taking weight loss injections affect IVF or fertility treatment?
Some fertility clinics have BMI thresholds for treatment, and some women use weight loss medicines to reach these targets.
If you are planning IVF or other fertility treatment, it is essential that your fertility clinic knows you are taking a weight loss medicine. They will advise when it needs to be stopped before treatment begins, in line with the wash-out periods above.
Do not continue weight loss injections into a fertility treatment cycle without specialist advice.
Weight loss injections, the menopause and HRT
Women in perimenopause can still become pregnant, so contraception is still needed until you are advised it can be stopped.
Hormone replacement therapy (HRT) is not a contraceptive. If you are taking HRT and could still become pregnant, you need a separate method of contraception while on a weight loss injection.
What SynovaMed will ask during your consultation
To keep you safe, if you could become pregnant, our clinical team will ask about:
- Whether you are pregnant, or could be pregnant
- Whether you are breastfeeding
- Whether you are planning a pregnancy
- What contraception you use
If you take an oral contraceptive and are prescribed Mounjaro, we will advise you about extra precautions after starting treatment and after each dose increase.
These questions are asked of every eligible patient. Please answer them honestly, as they are essential for safe prescribing.
You can find out more about our weight loss programme, including Mounjaro and Wegovy.
Frequently Asked Questions
Does Mounjaro affect the contraceptive pill?
Yes, it may. The MHRA advises that tirzepatide may reduce the effectiveness of oral contraceptives in people who are overweight or obese. Use a non-oral method, or add a barrier method, for 4 weeks after starting and 4 weeks after each dose increase.
Does Wegovy affect the contraceptive pill?
Wegovy is not currently considered to reduce the effectiveness of the pill in the same way as Mounjaro. However, vomiting or diarrhoea can affect pill absorption, and effective contraception is still required during treatment.
Can you get pregnant on Mounjaro?
Yes. Weight loss can improve fertility, and Mounjaro may reduce the effectiveness of the oral pill. Use effective contraception throughout treatment.
How long should I stop Mounjaro before trying to get pregnant?
The MHRA advises stopping Mounjaro at least 1 month before trying to conceive.
How long should I stop Wegovy before trying to get pregnant?
The MHRA advises stopping Wegovy at least 2 months before trying to conceive.
What should I do if I get pregnant on Wegovy or Mounjaro?
Stop taking the medicine, contact your GP or midwife, and inform your prescriber. Try not to panic and follow the advice of your healthcare team.
Can I take Mounjaro while breastfeeding?
No. Mounjaro and other weight loss injections are not recommended while breastfeeding.
What are "Ozempic babies"?
This is an informal term used to describe unexpected pregnancies in women taking GLP-1 medicines. Possible explanations include improved fertility from weight loss and, with Mounjaro, reduced effectiveness of the oral contraceptive pill.
What is the best contraception on Mounjaro?
Non-oral methods such as the implant, hormonal or copper coil, injection, patch or ring are not affected by changes in stomach emptying. The best choice depends on your health and preferences, so speak to your GP, sexual health clinic or pharmacist.
Do I need to use condoms on Mounjaro?
If you take the oral contraceptive pill, the MHRA advises adding a barrier method such as condoms, or switching to a non-oral method, for 4 weeks after starting and 4 weeks after each dose increase.
Can weight loss injections help with PCOS?
Weight loss may improve some PCOS symptoms and cycle regularity. However, weight loss injections are licensed for weight management, not specifically for PCOS or infertility.
The bottom line: weight loss injections, contraception and pregnancy
If you could become pregnant, contraception and pregnancy planning are an essential part of taking a weight loss injection safely.
The key points to remember are:
Do not use weight loss injections during pregnancy, while trying to conceive or while breastfeeding.
Use effective contraception throughout treatment.
If you take the pill and use Mounjaro, use a non-oral method or add condoms for 4 weeks after starting and after each dose increase.
Stop Wegovy at least 2 months, and Mounjaro at least 1 month, before trying to conceive.
If you become pregnant, stop the medicine and contact your GP or midwife.
Remember that weight loss can improve fertility, even if you have had difficulty conceiving before.
If you have any questions about contraception or pregnancy planning while taking a weight loss medicine, please contact our clinical team.
Medical Disclaimer
This article is intended for general educational purposes and does not replace personalised medical advice, diagnosis or treatment. Mounjaro, Wegovy and other prescription weight-management medicines are not suitable for everyone. Always follow the advice of your healthcare professional and read the patient information leaflets supplied with your weight loss medicine and your contraception. For personalised contraceptive advice, speak to your GP, a sexual health clinic or a pharmacist. If you think you may be pregnant, stop your weight loss medicine and seek medical advice.