Does Mounjaro Affect Contraception?

One of the most popular and effective weight loss injections available is Mounjaro. Clinical trials have shown that its active ingredient, tirzepatide, can help people lose on average 22.5% of their initial body weight in 72 weeks. It does this by mimicking the effects of 2 naturally produced hormones, called glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), to slow digestion, lower appetite, and regulate blood sugar levels.

An unexpected effect of Mounjaro is that it may reduce the effectiveness of some types of contraception. Up until June 2025, there were 40 reports of pregnancy to the Medicines and Healthcare products Regulatory Agency (MHRA) relating to GLP-1 medications. So, if you are currently taking Mounjaro and hormonal contraception, keep reading to find out if your fertility may be impacted.

Yes, there is some evidence to suggest that there is a link between Mounjaro and contraception being less effective, especially hormonal types taken by mouth like the contraceptive pill. That’s because Mounjaro slows down how quickly food moves through your stomach to help keep you feeling fuller for longer, but it can also mean less of the pill's ingredients (hormones) are absorbed.

It is this effect that raises concern about Mounjaro and pregnancy prevention when relying solely on oral hormonal contraceptives. If the synthetic versions of oestrogen and/or progesterone are not entirely absorbed, it can impact ovulation, cause irregular periods, and increase the chance of pregnancy.

Mounjaro side effects, like being sick and diarrhoea, can also affect the absorption of the pill, which may interfere with its effectiveness.

Not all types of contraception will be affected by Mounjaro. The main types of contraception that can be impacted are:

Combined oral contraceptives

The absorption of artificial oestrogen and progesterone in the pill can be reduced because of slowed stomach emptying.

Progesterone-only or mini pill

Because digestion is slowed down, the mini pill may be less effective as the active ingredients may not be fully absorbed.

Emergency contraceptive pills

The morning after pill, levonorgestrel, is also taken by mouth, so it may be less effective if stomach emptying is delayed. There is no evidence yet to confirm that Mounjaro affects ellaOne, but it may make it less effective.

Levonorgestrel may also be less effective if your BMI is over 26, so ellaOne may be a better choice. The copper IUD (coil) is the most effective form of emergency contraception, and can be inserted at sexual health clinics and by some GPs.

There does not appear to be any link between Mounjaro and contraception that bypasses the digestive system. So, any birth control method that does not rely on artificial hormones being delivered via the stomach or gut should remain fully effective, even when Mounjaro delays stomach emptying to aid weight loss.

The following contraception methods remain effective when they are used alongside Mounjaro:

Because these methods of contraception do not depend on the stomach or intestines for absorption, many doctors recommend switching to one of these methods while taking Mounjaro, rather than combining tirzepatide and oral contraceptives.

It is recommended that if you are taking tirzepatide and oral contraceptives, you add a barrier method, such as condoms, for 4 weeks after starting Mounjaro and after each dose increase to protect you against pregnancy.

Alternatively, you should switch from the contraceptive pill to a non-oral method, like the patch, ring, injection, implant or IUS/IUD.

➤ You can find out more in the Mounjaro patient information leaflet.

There may be a positive link between Mounjaro and fertility because weight loss in people who are obese or have medical conditions like polycystic ovary syndrome (PCOS) can improve the chances of getting pregnant.

Research suggests that weight loss can increase the chance of pregnancy by 21%, while weight loss interventions before IVF were found to increase the chance of natural conception by 47% in obese women.

So, weight loss, with or without the help of Mounjaro, can improve your fertility, which is something to consider if you are using oral contraceptives to prevent pregnancy.

Is Mounjaro safe during pregnancy?

No. Although Mounjaro can increase your chances of getting pregnant, you should not take it during pregnancy because there is not enough evidence to prove its safety, and the potential risks to unborn babies are unknown.

Animal studies have found that tirzepatide caused birth defects and reduced growth in foetuses. There are no similar studies in humans for ethical reasons, but one study, in which 6 people accidentally became pregnant, reported that there was:

• 1 healthy child
• 1 spontaneous abortion (miscarriage)
• 1 ectopic pregnancy
• 1 elective termination (voluntary abortion)
• 2 pregnancies with no outcomes reported

If you become pregnant while taking Mounjaro, stop taking it and contact your doctor straight away. They will need to report your pregnancy to an organisation that monitors drug toxicity during pregnancy. You’ll also be offered a detailed 20-week scan as standard to make sure your baby is developing properly, but no extra monitoring should be required.

When should I stop taking Mounjaro if I want to get pregnant?

If you are taking Mounjaro for weight loss or type 2 diabetes and want to get pregnant, you should stop taking it at least 1 month before you plan to start trying for a baby. This will allow enough time for tirzepatide to leave your system completely.

In answer to the question, ‘Does Mounjaro affect birth control?’ The simple answer is yes, if you take oral hormonal contraceptives, like the combined or mini pill, or if you need to take the emergency contraceptive pill.

Because these types rely on your stomach or intestines for absorption, they may be less effective when you take Mounjaro because one of its main actions is to slow down digestion. This can mean the active ingredients in the pill may not be fully absorbed, and you could get pregnant.

Instead, to support pregnancy prevention, you should consider switching to a hormonal contraceptive that does not need to be taken via the mouth and digestive system, like the patch, vaginal ring, injection, or implant, or add a barrier method, like condoms, to your current pill routine.

Because Mounjaro and fertility changes can increase the chances of pregnancy, effective contraception is essential if you are not planning on having a baby.