Introduction
Medicines such as Wegovy (semaglutide) and Mounjaro (tirzepatide) are increasingly used to help people lose weight and manage blood sugar. If you are using contraception or planning a pregnancy, it is important to understand how these medicines may affect oral birth-control tablets and what steps to take to stay protected and plan safely.
How GLP-1 Medicines Interact with Oral Contraceptives
GLP-1 medicines delay gastric emptying — they slow the rate at which food and tablets leave the stomach (1). This means oral contraceptive pills may take longer to absorb, and in some cases, the amount absorbed into the bloodstream may be slightly lower.
Tirzepatide (Mounjaro)
Studies show that tirzepatide can reduce blood levels of ethinylestradiol and levonorgestrel by about 20% after the first dose (2).
The effect is strongest during the first four weeks of treatment and after each dose increase because gastric emptying is most delayed at these times. For this reason, additional contraception (for example condoms) or a non-oral method is recommended for four weeks after starting or increasing the dose (3).
Semaglutide (Wegovy):
Semaglutide also slows digestion but to a lesser degree and for a shorter time. Clinical studies found no meaningful reduction in contraceptive hormone levels (4). Therefore, additional contraception is only required if you experience vomiting or diarrhoea, which can prevent tablets from being absorbed (3).
Contraceptive Methods Not Affected by GLP-1 Medicines
Contraceptives that aren’t taken by mouth, bypass the stomach and are not affected by delayed gastric emptying:
- Intrauterine device (IUD) (copper coil)
- Contraceptive patch or vaginal ring
- Progestogen injection (Depo-Provera or Sayana Press)
- Implant (Nexplanon)
These methods remain reliable during GLP-1 treatment and are often preferred if long-term contraception is required.
If you're interested in learning more about these options or finding the one that's right for you, please speak to your doctor, nurse, or sexual health clinic.
Birth Planning and Pregnancy Considerations
GLP-1 medicines are not recommended during pregnancy or breastfeeding (5).
If you are planning to conceive, you should stop GLP-1 treatment well in advance to allow the medicine to clear from your body.
- For semaglutide (Wegovy), stop at least two months before trying for pregnancy.
- For tirzepatide (Mounjaro), stop at least one month before conception (5).
Weight loss before pregnancy can improve fertility and pregnancy outcomes, but losing weight too quickly may temporarily affect menstrual cycles.
Discuss family planning with your GP or prescriber before initiating GLP-1 therapy.
What Patients Should Consider:
1.Before starting treatment
- Inform your prescriber which type of contraception you use. If you are using an oral contraceptive, plan to use extra protection for four weeks after starting your weight loss medication and four weeks after any tirzepatide dose increases.
- Consider switching to a non-oral method for maximum reliability.
2.During treatment / Maintenance
If you experience vomiting or diarrhoea, use additional contraception for seven days after symptoms stop.
- Keep a record of your injection schedule so you know when extra precautions are needed.
- Report any missed periods or signs of pregnancy promptly.
If you plan to become pregnant, you must discuss stopping your GLP-1 medicine with your GP or weight-management prescriber.
Wait for the recommended time (at least one-two months, depending on the drug as per the guidance above) before trying to conceive.
- Continue taking folic acid and follow pre-conception advice.
3. When to Seek Medical Advice
Contact your GP or pharmacist if you:
- Miss a period or suspect pregnancy while on treatment.
- Have persistent vomiting or diarrhoea lasting more than 24 hours.
- Experience severe abdominal pain or unexplained vaginal bleeding
If symptoms are severe, call 111 or 999 in an emergency.
Summary
GLP-1 medicines can influence the absorption of oral contraceptives, especially tirzepatide (Mounjaro), because of their stronger effect on gastric emptying.
To stay protected:
- Use non-oral or barrier contraception for four weeks after starting or increasing tirzepatide.
- With semaglutide, use extra precautions only if you are vomiting or have diarrhoea.
- Stop GLP-1 treatment well before pregnancy and plan conception with your healthcare team.
With careful planning and clear communication, GLP-1 treatment and birth control can be managed safely together.
References
- Drucker DJ. The cardiovascular biology of glucagon-like peptide-1. Cell Metab. 2016;24(1):15–30.
- Lilly. Tirzepatide Clinical Pharmacology Study Report: Effect on Oral Contraceptive Pharmacokinetics. Data on file; 2023.
- Faculty of Sexual and Reproductive Healthcare (FSRH). GLP-1 Agonists and Oral Contraception Guidance. Jan 2025.
- Wegovy (semaglutide) Summary of Product Characteristics. Novo Nordisk Ltd; 2024.
- Mounjaro (tirzepatide) Summary of Product Characteristics. Eli Lilly Ltd; 2024.
- Primary Care Women’s Health Forum (PCWHS). Injectable Weight-Loss Drugs, Contraception and HRT. Apr 2025.