Mounjaro (tirzepatide) is a GLP-1 and GIP receptor agonist licensed in the UK for type 2 diabetes and weight management. For people of reproductive age, understanding how Mounjaro and birth control interact is essential. Tirzepatide slows gastric emptying, which can reduce the absorption of oral contraceptive pills during the first four weeks of treatment and after dose increases. The UK Summary of Product Characteristics advises switching to non-oral contraception or adding barrier methods during this period. This article explains which contraceptive methods remain effective with Mounjaro and how to maintain reliable pregnancy prevention.

How Mounjaro May Affect Birth Control Effectiveness

Mounjaro (tirzepatide) is a glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptor agonist licensed in the UK for the treatment of type 2 diabetes mellitus and, more recently, for weight management in adults with obesity (BMI ≥30 kg/m²) or overweight (BMI ≥27 kg/m²) with weight-related comorbidities. One important consideration for people of reproductive age is the potential interaction between Mounjaro and hormonal contraception.

Mounjaro can reduce the effectiveness of oral contraceptive pills during the initial weeks of treatment. This occurs because tirzepatide slows gastric emptying—a key part of its mechanism of action that helps regulate blood glucose and promote satiety. When the stomach empties more slowly, the absorption of orally administered medications, including combined oral contraceptives (COC) and progestogen-only pills (POP), may be delayed or reduced. This effect is most pronounced during the first four weeks of Mounjaro treatment or following dose escalation, when gastrointestinal effects are typically strongest.

The UK Summary of Product Characteristics (SmPC) for Mounjaro advises that people using oral contraceptives should switch to a non-oral method or add a barrier method (such as condoms) for at least four weeks after starting Mounjaro and after each dose increase. This precaution is essential to prevent unintended pregnancy. It is important to note that there is no official evidence suggesting Mounjaro directly affects the hormonal activity of contraceptives; rather, the concern centres on reduced gastrointestinal absorption. Patients should discuss their contraceptive needs with their GP or specialist before commencing tirzepatide therapy to ensure continuous, reliable pregnancy prevention.

Which Contraceptive Methods Are Safe with Mounjaro

Not all contraceptive methods are affected by Mounjaro's impact on gastric emptying. Non-oral hormonal contraceptives and barrier methods remain fully effective and do not require additional precautions when used alongside tirzepatide. Understanding which options are unaffected can help maintain reliable contraception without interruption.

Long-acting reversible contraceptives (LARCs) are considered the gold standard and are entirely safe to use with Mounjaro. These include:

• Intrauterine devices (IUDs): Both the copper IUD (non-hormonal) and the levonorgestrel-releasing intrauterine system (LNG-IUS, such as Mirena or Kyleena) are unaffected, as they deliver contraception locally within the uterus rather than relying on gastrointestinal absorption.

• Contraceptive implant (Nexplanon): This subdermal progestogen implant releases etonogestrel steadily into the bloodstream and is not influenced by gastric emptying.

• Contraceptive injection (Depo-Provera): Administered intramuscularly every 12–13 weeks, this progestogen injection bypasses the digestive system entirely.

Barrier methods such as male or female condoms, diaphragms, and cervical caps are also safe and effective when used correctly with Mounjaro. These methods do not involve hormones or absorption. It's important to note that only male and female condoms provide protection against sexually transmitted infections (STIs).

Transdermal patches and vaginal rings (such as the combined contraceptive patch or NuvaRing) deliver hormones through the skin or vaginal mucosa, avoiding the gastrointestinal tract. There is no evidence that Mounjaro affects these methods, and additional precautions are not required for non-oral methods. NICE guidance emphasises shared decision-making in contraceptive choice, taking into account individual preferences, medical history, and lifestyle factors.

What to Do If You're Taking Both Mounjaro and Contraception

If you are currently taking Mounjaro and using oral contraception, it is essential to take proactive steps to maintain effective pregnancy prevention. The key recommendation is to use additional contraceptive protection during the period when Mounjaro may interfere with pill absorption.

For the first four weeks after starting Mounjaro and for four weeks following each dose increase, people taking oral contraceptive pills should either:

• Switch to a non-oral contraceptive method (such as an IUD, implant, injection, patch, or ring), or

• Use a reliable barrier method (such as condoms) in addition to their oral contraceptive pill.

This precaution applies to both combined oral contraceptives and progestogen-only pills. After the initial four-week period, if no further dose adjustments are planned, oral contraceptives may be continued as usual.

If you miss a contraceptive pill or experience vomiting or severe diarrhoea while taking Mounjaro, follow the specific missed pill rules for your contraceptive method. These rules differ between combined pills, traditional progestogen-only pills, and desogestrel or drospirenone progestogen-only pills. Refer to your pill's patient information leaflet or the Faculty of Sexual and Reproductive Healthcare (FSRH) guidelines. Gastrointestinal side effects are common with Mounjaro, particularly nausea, vomiting, and diarrhoea, which can further compromise oral contraceptive absorption.

Speak to your GP, practice nurse, or sexual health clinic if you have any concerns about your contraception while using Mounjaro. They can help you choose the most appropriate method and provide emergency contraception if needed. If you suspect you may be pregnant or have had unprotected intercourse, seek advice promptly. Emergency contraception options include the copper IUD (most effective), levonorgestrel or ulipristal acetate. If using ulipristal acetate, you should delay restarting hormonal contraception for 5 days and use condoms during this time. If you experience vomiting within 3 hours of taking oral emergency contraception, you may need to repeat the dose.

If you experience side effects from Mounjaro, report them through the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk or the Yellow Card app).

Alternative Contraception Options While Using Mounjaro

For people starting or continuing Mounjaro, switching to a non-oral contraceptive method offers the most reliable protection without the need for additional precautions or concern about drug interactions. Several highly effective alternatives are available through the NHS, and your GP or sexual health service can help you select the most suitable option.

Long-acting reversible contraceptives (LARCs) are recommended by NICE as first-line options due to their high efficacy (over 99%), convenience, and independence from user adherence. The levonorgestrel intrauterine system (LNG-IUS) is particularly popular, offering effective contraception for three to six years (depending on the device) and often reducing menstrual bleeding. The copper IUD is a non-hormonal option effective for up to ten years and is suitable for those who prefer to avoid hormones altogether. The contraceptive implant lasts for three years and is discreet, while the contraceptive injection requires administration every three months.

Barrier methods such as condoms remain an important option, especially for those who prefer non-hormonal, on-demand contraception or wish to protect against STIs. While slightly less effective than LARCs when used alone (around 82–98% effective with typical use), condoms are widely accessible and have no medical contraindications.

Permanent contraception (female sterilisation or male vasectomy) may be considered for individuals or couples who have completed their families, though this is an irreversible decision requiring careful counselling.

It is worth noting that weight loss and improved glycaemic control with Mounjaro may increase fertility, particularly in people with polycystic ovary syndrome (PCOS), making reliable contraception even more important if pregnancy is not desired.

According to the UK SmPC, Mounjaro is not recommended during pregnancy, and people planning to conceive should discontinue tirzepatide at least one month before attempting pregnancy. If you are planning a pregnancy or discover you are pregnant while taking Mounjaro, contact your GP or diabetes specialist immediately. Your healthcare team can provide tailored advice on contraception, family planning, and the safe use of Mounjaro in the context of your reproductive health.

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