Are you taking or considering taking weight loss injections, but rely on the oral pill for contraception? If so, this vital information is for you. In June 2025, the UK’s medicines regulatory board, MHRA, released guidance on the use of weight loss injections for women, urging them to use “effective contraception” because of the lack of data on safety in pregnancy.
However, in this guidance they also warned that Mounjaro, a popular medical weight loss injection containing tirzepatide, had been found to reduce the effectiveness of the oral contraceptive pill in some women. This hit the headlines, as some women found themselves pregnant despite taking the daily pill.
If you’re considering using weight loss injections and currently rely on the contraceptive pill, it’s important to understand how these treatments interact. The National Health Service (NHS) have recently updated their guidance on the use of GLP-1 agonist medications when taken alongside oral contraception.
At Bodyline, we prescribe medical weight loss treatments within fully supported programmes, providing guidance and advice throughout a weight loss journey.
We’ve put together a handy guide with everything you need to know about weight loss injections and the oral pill.
GLP-1 weight loss injections: the medications available
GLP-1 agonists are a group of prescription medications originally developed for type 2 diabetes but now widely used to support weight loss.
Commonly prescribed GLP-1 agonists include:
These medications can only be prescribed by a qualified healthcare professional to those eligible and are not available over the counter. Eligibility depends on medical history, weight health markers such as blood pressure or waist circumference, and whether a person lives with weight related comorbidities or conditions. Most importantly, however, eligibility is based on a person’s Body Mass Index (BMI).
A patient must fall under the category of obese with a BMI of more than 30kg/m2, or under the category of overweight (BMI of more than 27kg/m2) WITH a weight related health problem such as high blood pressure, prediabetes, or otherwise. If you are not sure if you are eligible, call us today on 0800 995 6036 and speak to a member of our specialist weight health customer service team.
Each weight loss medication works slightly differently, but all aim to help people lose weight by influencing appetite and digestion.
How do GLP-1 weight loss injections work?
GLP-1 agonists mimic the action of a natural hormone called glucagon-like peptide-1.
One of their main effects is to slow down the rate at which food leaves the stomach—a process known as delayed gastric emptying. This not only helps you feel fuller for longer but also reduces appetite and can lead to significant weight loss.
Mounjaro is slightly different though, it has an additional mechanism working alongside the GLP-1 agonists. It includes GIP agonists, which is mimicking the action of the glucose-dependent insulinotropic polypeptide hormone working similarly to slow down the gastric emptying and regulate blood sugar levels.
The delayed gastric emptying effect seen in Mounjaro is also central to how these medications can interact with other oral drugs, such as the contraceptive pill.
Do all weight loss injections impact the contraceptive pill?
Not all GLP-1 weight loss injections affect the contraceptive pill in the same way.
According to current NHS and MHRA guidance, there is no evidence that GLP-1 agonists including semaglutide (WeGovy or Ozempic) and liraglutide (Saxenda) reduce the effectiveness of oral contraception. If you are taking one of these medications alongside your pill, there is no current advice that you should take additional contraceptive precautions.
However, it’s important to highlight that if you experience vomiting or severe diarrhoea as a side effect of your medical weight loss injections, this can affect absorption of the pill.
“If vomiting occurs within three hours of taking the contraceptive pill, or severe diarrhoea occurs for more than 24 hours, you should follow the guidance for missed pills.” – The Faculty of Sexual and Reproductive Healthcare guidance
Last year the Guardian reported that people on weight-loss drugs had contributed to an unexpected baby boom. There was even a Facebook group called “I got pregnant on Ozempic” which had more hundreds of members at the time. It is unclear what caused this boom specifically.
Mounjaro and the contraceptive pill
Tirzepatide (Mounjaro) is an exception. That’s because, as we just explained, Mounjaro works slightly differently to the other medications.
If you start tirzepatide or increase your dose, you are advised to use a barrier method of contraception, such as condoms, in addition to your pill for four weeks following.
Dr Morgan Toerien is a weight, health, and wellness practitioner at Bodyline Clinics:
“The big reason that we want to make sure that people are using appropriate contraception while they’re on GLP-1s is because we haven’t yet confirmed that they’re completely safe for use in pregnancy.
As a rule, most oral contraceptives work fairly well with the older type of GLP-1s, but with tirzepatide, which is Mounjaro, it seems that – particularly around starting the dose or increasing the dose – there can be less efficacy of the oral contraceptive.
Like with many medications, it’s always a good idea to use alternate methods of contraception for at least four weeks after starting the medication or changing the dose. Barrier methods [like condoms] are safe, but patients may want to consider options like injectable contraceptives, IUDs and implants, which don’t seem to be affected at all.”
Why does Mounjaro make the pill less effective?
Mounjaro specifically has a more pronounced and longer-lasting effect on delaying gastric emptying compared to other GLP-1 agonists.
This delay can reduce the absorption of oral medications, including the contraceptive pill, making it less effective at preventing pregnancy—especially during the first four weeks of treatment or after any dose increase.
Clinical data has shown that tirzepatide can significantly reduce the bioavailability of oral contraceptives, prompting both manufacturers and health authorities to recommend extra contraceptive precautions during these periods.
If you switch from another GLP-1 agonist to tirzepatide, the same advice applies to use a barrier method like condoms for four weeks after the change and after any dose increase.
What if I want to get pregnant while using weight loss injections?
GLP-1 agonists are not recommended during pregnancy, and it’s important to use effective contraception while taking these medications. The MHRA explain this is vital because there is not enough safety data to know whether taking the medicine could cause harm to the baby.
If you are planning a pregnancy, you will need to stop your weight loss injection and allow for a “washout period” before trying to conceive. This means waiting for an appropriate length of time to ensure the medication is no longer in your system.
The recommended washout period varies by medication: one month for tirzepatide and two months for semaglutide. This ensures the medication is cleared from your system and reduces any potential risk to the developing baby.
If you become pregnant while taking a GLP-1 agonist, contact your doctor as soon as possible to discuss the next steps.
Why is supported medical guidance important?
Every individual’s health circumstances are unique, and the choice of weight loss medication should always be made in consultation with a qualified healthcare professional. At Bodyline Clinic, our specialist weight loss clinical staff work with each patient to create a personalised weight loss plan based on their medical history, lifestyle, and as guidance is updated, their reproductive health and choices.
If your situation changes while using GLP-1 agonist weight loss injections, and either you become pregnant or you wish to conceive, at Bodyline we work alongside you to ensure your medical weight loss treatment works to help you boost the quality of your life.
It is always advisable to consult with the medical professionals who prescribed your weight loss injections to ensure your safety and health while coming off the medication.
The NHS and Faculty of Sexual and Reproductive Health stress that no contraception is 100% effective, and individual factors—such as side effects like vomiting or diarrhoea—can impact the reliability of the pill. If you experience ongoing digestive side effects while using a GLP-1 agonist, or if you’re unsure about which contraceptive method is right for you, our experienced specialist nurses are trained to offer guidance and advice for your safety.
Bodyline Works, Bodyline Cares
Bodyline has been offering medical weight loss treatments for almost 20 years, and every patient has a unique reason as to why they have come to us.
Our programmes are built holistically around your personal goals, so if you are seeking medical weight loss treatment with a goal of improving your fertility and likelihood of pregnancy, we urge you to get in touch and consider speaking to one of our experienced staff members. They can guide you through from the very first consultation, to the moment you want to start trying to conceive, ensuring every decision made is with the safety and wellbeing of you and your future in mind.
Get in touch with Bodyline today to find out more about our safe, supported and effective weight health programmes. Call us on 0800 995 6036 or fill in an online contact form for a call back.Call 0800 995 6036 or complete a contact form for a call back.
Contact Bodyline today to find out more about our safe and effective weight loss programmes and range of treatment options.
