Medications for weight management, such as Wegovy (semaglutide) and Mounjaro (tirzepatide), are becoming increasingly common, particularly among women of reproductive age. With this rise in use, many patients are now asking whether these treatments have any effect on the effectiveness of their contraception.
Some medicines can interfere with contraception, but potential interactions with newer treatments like Wegovy and Mounjaro are less well known.
In this blog, we look at what current research and official guidance say about these medications and their potential impact on different forms of birth control, helping you make safe and informed decisions about your health.
How Wegovy and Mounjaro Work?
| Medication | How It Works | Key Benefits | Results |
| Wegovy (semaglutide) | Mimics the GLP-1 hormone, which regulates appetite and digestion. Slows stomach emptying, keeps you fuller for longer, and reduces cravings. | Supports weight loss by helping you eat less and manage your appetite more effectively. | Up to 21% weight loss with lifestyle changes. |
| Mounjaro (tirzepatide) | Targets two hormones, GLP-1 and GIP. This dual action reduces appetite, improves how the body handles sugar, and promotes weight loss. | Helps with both weight management and blood sugar control, often more effective for some people than GLP-1 medicines alone. | Up to 23% weight loss is one of the most effective options. |
Why Interactions With Birth Control Matter?
For many women, contraception is a trusted and essential part of daily healthcare, so any medication that might influence its effectiveness deserves careful attention. Evidence suggests that tirzepatide (the active ingredient in Mounjaro) may have a stronger effect on the absorption of oral contraceptives compared to some other GLP-1 receptor agonist medicines. This means that, for women relying on hormonal contraception, it is important to understand how these treatments may influence reliability.
There are several possible reasons why weight management injections could impact birth control:
- Hormonal balance: Achieving a healthier weight can support natural hormone regulation, which may increase the chances of pregnancy even when using contraception.
- Digestive side effects: Wegovy and Mounjaro can cause nausea, vomiting, or diarrhoea. If the contraceptive pill is not fully absorbed due to these side effects, its effectiveness may be reduced.
- Delayed absorption: These medications slow the rate at which food leaves the stomach. This delay may also affect how well oral contraceptive hormones are absorbed into the body.
Understanding these potential factors is important to ensure contraception remains effective and to know when additional precautions may be needed.
Do Semaglutide and Tirzepatide Affect Birth Control?
Both semaglutide (the active ingredient in Wegovy) and tirzepatide (the active ingredient in Mounjaro) work by slowing down the rate at which food leaves the stomach. This delayed gastric emptying can also influence how other oral medications are absorbed, including contraceptive pills.
Clinical guidance indicates that tirzepatide may have a greater effect on oral contraceptive absorption than semaglutide. For this reason, some women are advised to use an additional form of contraception, particularly when starting treatment or adjusting their dose. By contrast, semaglutide has not been shown to significantly reduce contraceptive effectiveness, although caution is still recommended if digestive side effects like vomiting or diarrhoea occur.
It is also important to note that these potential interactions apply mainly to oral contraceptives. Other forms of birth control, such as patches, vaginal rings, injections, implants, or intrauterine devices (IUDs), are not affected in the same way.
In practice, this means women using oral contraception while on Wegovy or Mounjaro should monitor for side effects, speak with their healthcare provider, and consider backup protection if advised.
Are Non-Oral Contraceptives Affected by Wegovy and Mounjaro?
The possible interaction between weight management injections and contraception mainly relates to oral contraceptive pills, as their effectiveness depends on proper absorption in the digestive system. Other methods of contraception are not processed in the same way and are therefore not affected in the same manner.
- Contraceptive patch and vaginal ring: These deliver hormones through the skin or vaginal lining, bypassing the digestive system. Their effectiveness is not reduced by semaglutide or tirzepatide.
- Injections and implants: These provide a steady release of hormones directly into the bloodstream. Because they do not rely on absorption from the stomach, they remain effective while using Wegovy or Mounjaro.
- Intrauterine devices (IUDs): Both hormonal and non-hormonal (copper) IUDs work locally in the uterus. Their contraceptive action is not influenced by weight loss medications.
- Barrier methods: Options such as condoms, diaphragms, or caps work mechanically and are unaffected by any medication.
For women who experience persistent side effects like nausea, vomiting, or diarrhoea while on Wegovy or Mounjaro, non-oral contraceptive methods may offer extra reassurance and reliability.
Can Switching From Mounjaro to Wegovy Affect Birth Control?
Some patients may be advised to switch from Mounjaro (tirzepatide) to Wegovy (semaglutide), depending on treatment goals, availability, or side effect management. When making this change, it’s natural to wonder whether contraceptive effectiveness could also be impacted.
The main difference lies in how each medication affects oral contraceptive absorption. Evidence suggests that tirzepatide may have a stronger effect on reducing the absorption of the pill compared to semaglutide. As a result, women moving from Mounjaro to Wegovy may face a lower level of interaction risk.
Another point to note is that a higher-dose version of Wegovy (7.2 mg) is expected to become available this year. While no major contraceptive interactions are anticipated beyond those already associated with semaglutide, patients starting or switching to this dose should still follow professional advice and monitor for side effects that could impact pill absorption.
Common Side Effects That May Indirectly Affect Birth Control
Both Wegovy and Mounjaro belong to a class of medicines that can cause digestive side effects, especially when treatment first begins or when the dose is increased. While these side effects are usually temporary and manageable, they may reduce the effectiveness of oral contraceptive pills if the hormones are not fully absorbed.
The most relevant side effects include:
- Nausea and vomiting: If vomiting occurs soon after taking the pill, there may not be enough time for the hormones to enter the bloodstream.
- Diarrhoea: Persistent diarrhoea can also reduce absorption, making the pill less reliable.
- Reduced appetite or slower digestion: These are less likely to interfere directly but may still affect the timing of absorption in some women.
It’s important to follow the same guidance you would if you were sick while on the pill. This may mean taking another pill, using backup contraception, or seeking advice from a healthcare professional. Non-oral methods of contraception, such as the patch, implant, or IUD, are not influenced by these side effects and can offer added reassurance.
Recommendations From Healthcare Professionals
At The Care Pharmacy, our clinical team is here to guide you through safe use of medications like Wegovy and Mounjaro while ensuring your contraception remains reliable. We review your current method, monitor for side effects, and advise on the best options for your individual needs.
Key recommendations include:
- Consult First: Discuss your contraception with your GP, pharmacist, or The Care Pharmacy specialist before starting treatment.
- Use Backup if Needed: If you rely on the pill, consider condoms during the first four weeks, after dose changes, or if vomiting/diarrhoea occurs.
- Consider Alternatives: Implants, injections, patches, rings, and IUDs are unaffected by these medicines and may offer reassurance.
- Monitor Side Effects: Report digestive side effects early to check if backup contraception is necessary.
- Review During Switches: Moving from Mounjaro to Wegovy, or starting the new Wegovy 7.2 mg dose, should prompt a contraception review.
The Care Pharmacy will work with you to make sure your weight management journey does not compromise contraceptive safety.
References
FAQs
Do Wegovy or Mounjaro reduce the effectiveness of birth control pills?
Yes, particularly with Mounjaro (tirzepatide), studies suggest it may reduce the absorption of oral contraceptives. Wegovy (semaglutide) appears to have less impact, but both can cause digestive side effects that may affect pill reliability.
What cancels out the birth control pill?
Anything that prevents full absorption of hormones, such as vomiting, diarrhoea, or interactions with certain medicines (like some antibiotics or epilepsy drugs), can reduce pill effectiveness.
Is it safe to take contraceptives while on Mounjaro or Wegovy?
Yes, but it’s important to choose the right method. Non-oral options like implants, injections, IUDs, patches, or vaginal rings are unaffected and may offer greater reassurance compared to the pill.
Can GLP-1 weight loss injections cause unplanned pregnancy risks?
Yes, indirectly. By reducing pill absorption or through side effects like vomiting/diarrhoea, GLP-1 medicines (Wegovy, Mounjaro, Ozempic) may lower contraceptive reliability, which could increase the chance of an unplanned pregnancy.
Do I need backup contraception while starting Mounjaro or Wegovy?
Yes, if you use the pill. It’s often recommended to use a barrier method (such as condoms) for the first 4 weeks of treatment, after dose increases, or if digestive side effects occur.
Are IUDs or implants affected by Wegovy or Mounjaro?
No. IUDs (hormonal or copper), implants, patches, rings, and injections bypass the digestive system and are not affected by these weight loss injections.
Does Wegovy affect periods or menstrual cycles?
Some women report changes to their menstrual cycle, often related to weight loss and hormonal shifts rather than Wegovy itself. These changes are usually temporary but should be discussed with your GP if persistent.
Can Mounjaro affect fertility in women?
Yes, weight loss and improved insulin sensitivity from Mounjaro can restore ovulation and fertility in some women, especially those with PCOS. This means women may be more likely to conceive if contraception is not reliable.
What birth control methods are safest while using GLP-1 injections?
Non-oral methods such as implants, injections, IUDs, patches, or vaginal rings are the safest choices, as they are not affected by digestive absorption issues.
What is the new warning on Mounjaro?
Recent updates highlight a potential interaction with oral contraceptives, particularly in the early stages of treatment or after dose changes. Women on the pill are advised to use backup contraception during these times.
Should I talk to my doctor before mixing birth control with Wegovy or Mounjaro?
Absolutely. Always consult your GP or pharmacist before starting these injections if you are on hormonal contraception. They can guide you on the safest method for your situation.
Do vomiting and diarrhoea make the contraceptive pill less effective?
Yes. If vomiting or severe diarrhoea occurs within a few hours of taking the pill, hormones may not be fully absorbed, reducing effectiveness. Backup contraception may be needed.
Can I use emergency contraception on Wegovy?
Yes. Emergency contraception (such as the morning-after pill or copper IUD) can be used if needed. If you vomit within 3 hours of taking the morning-after pill, you may need another dose, so always seek pharmacy advice.
