Mounjaro and contraception: what every woman should know

Somewhere in your Mounjaro patient leaflet is a line about oral contraceptives. It is easy to miss. But it is important that you take note of it.

In June 2025, the MHRA issued its first public alert specifically about contraception and weight loss injections.

It followed reports of unexpected pregnancies in women taking the injections, and some of those women were also using contraception at the time.

The alert explains that Mounjaro may make oral contraceptives less effective in people who are overweight or living with obesity.

There is not enough safety data on any of these medicines to know whether they could harm a developing baby.

A 2026 study also suggests that losing a significant amount of weight can restore ovulation in women whose cycles had become irregular or stopped altogether, which changes the odds of conceiving.

This guide covers if contraception is safe to use while on Mounjaro, which contraceptive methods are the most reliable on Mounjaro, when you should avoid using contraception on Mounjaro, and what to do if contraceptive methods fail on Mounjaro.

Before you begin: A little bit about OnlineClinic

OnlineClinic has been operating since 2011 and has treated more than 2.1 million patients.

The pharmacy is registered with the General Pharmaceutical Council (GPhC), our prescribers are registered with the General Medical Council (GMC), and the service is regulated by the Care Quality Commission (CQC).

As of August 2026, on Trustpilot, the service rating is 4.6 out of 5 based on 6,451 reviews.

The MHRA published guidance on GLP-1 medicines in June 2025 and last updated it in February 2026. On contraception and weight loss injections, it says two things:

First, everyone who could become pregnant needs reliable contraception while taking any GLP-1 medicine.

These medicines include Mounjaro, Wegovy, Ozempic, Rybelsus, Saxenda, and Victoza.

The reason is not that these medicines cause pregnancy.

It is that there is not enough human safety data to know whether they could harm a developing baby, so pregnancy needs to be avoided while you are on treatment.

Second, there is extra advice that applies to Mounjaro alone.

If you take an oral contraceptive and you are overweight or living with obesity, the MHRA advises you to either:

• Add a barrier method (condoms) for four weeks after starting Mounjaro, and again for four weeks after any increase in dose, or
• Switch to a non-oral method such as the coil or the implant, which the guidance describes as more likely to stay effective alongside a GLP-1 medicine

The Faculty of Sexual and Reproductive Healthcare, now the College of Sexual and Reproductive Healthcare, published a statement saying the same thing in February 2025.

It adds one detail worth holding onto. Of all the medicines in this class, tirzepatide is the only one shown to affect oral contraception.

Mounjaro's active ingredient is tirzepatide. Part of how it works is by mimicking two gut hormones, GLP-1 and GIP, and slowing down how quickly your stomach empties into your gut.

That is what makes you feel full sooner and stay full longer, and it is also why nausea is the most common early side effect of taking this medicine. We cover that timeline in Mounjaro side effects week by week.

Anything you swallow gets caught up in the same slowdown.

A pill sits in your stomach for longer, so the hormone inside it trickles into your bloodstream instead of arriving in one go.

To see why that matters, it helps to know what the pill is actually doing.

Getting the hormone into you is not enough on its own. The pill has to lift the level in your blood past a certain point and hold it there, because that is what stops your ovaries releasing an egg.

Absorb the same dose too slowly and you can fall short of that point, even though none of the hormone has gone missing.

So the number that matters here is not how much of the pill you absorb. It is how high the level gets.

Here is what the study behind the warning found.

40 healthy women took a full cycle of the combined pill on its own, then a second cycle with a single 5mg dose of tirzepatide added. Researchers measured the pill's hormones in their blood through both cycles.

With tirzepatide added, the hormone levels reached only a third to a half of the peak they had reached without it.

Those peaks also arrived 2.5 to 4.5 hours later than they had without tirzepatide.

The total amount of hormone absorbed over 24 hours fell by much less than the peaks did, to around a fifth below the level measured without tirzepatide.

So most of the hormone still reached the bloodstream. It simply never built to a high enough level at any single moment.

Here’s the standard rule: If the contraceptive method has to be absorbed through the stomach, it can be affected. If it does not, it cannot.

Keeping this in mind, here is a list of all the contraceptive methods that can be affected by Mounjaro, and those that cannot be affected.

If you are on the patch, the ring, an implant, an injection, or either type of coil, the pill interaction is not your issue.

You still need to keep using your method reliably, because pregnancy has to be avoided on Mounjaro either way. But you do not need to add a second method.

If you are on the combined pill or a mini pill, the four-week rule applies to you.

Mounjaro is not one dose.

In the UK, it is escalated through six doses, and you spend at least four weeks at each one before moving up.

We go into detail about each dose in Mounjaro dosage schedule explained.

The four-week contraception window applies to each of those increases.

So if you move up on the earliest possible schedule, the windows sit end to end:

The consequence is that someone climbing from 2.5mg to 15mg at the fastest permitted pace needs continuous backup contraception for around five to six months, not four weeks.

The four-week window only becomes a genuine four weeks once you settle on a dose and stay there.

That is why switching to a non-oral method can be simpler than tracking windows.

It is not that the pill stops working on Mounjaro.

It is that keeping track of which four weeks you are in, every time your dose changes, is easy to get wrong.

One more thing restarts the clock.

If you move to Mounjaro from Wegovy or another GLP-1 medicine, your first Mounjaro injection starts a four-week window even though you have been on treatment for months.

The advice attaches to tirzepatide, not to being on a weight loss injection in general, so it is worth raising when the switch is being discussed rather than after.

Planning to switch to Mounjaro from Wegovy? Check out our complete guide.

Slowed absorption is not the only way the pill can fail on Mounjaro.

There is a second and separate risk.

Vomiting and diarrhoea are common on Mounjaro, particularly in the first few weeks and after a dose increase.

If you are sick or have severe diarrhoea, a pill you have swallowed may never be absorbed at all.

This has nothing to do with tirzepatide specifically. It is true of any pill, any time you are unwell.

The standard missed-pill rules apply here:

• If you vomit within two to three hours of taking your pill, treat it as a missed pill and follow the missed-pill instructions in your leaflet
• If you have severe diarrhoea lasting more than 24 hours, treat each day as a missed pill
• If sickness or diarrhoea continues for more than a couple of days, use condoms until you have taken seven days of pills without being unwell

This is where the two risks stack. A dose increase brings both a fresh absorption window and a higher chance of nausea, at the same time.

This means you have to be very careful in the first 15 days after a dose change.

If sickness is a recurring problem for you rather than an occasional one, talk about it with your prescriber. A dose that makes you regularly sick may need to be reviewed.

Weight and ovulation are closely linked.

Carrying excess weight can stop ovulation happening reliably, which is one reason women with polyendocrine metabolic ovarian syndrome (PMOS) so often have irregular or absent periods.

When weight comes down, ovulation frequently comes back.

The clearest recent figure comes from a UK trial reported in 2026.

Among women with PMOS and a BMI of 35 or above, ovulation returned in 19% of those who lost no weight, and in more than half of those who did.

Two caveats.

Neither the MHRA alert nor Mounjaro's product information addresses this, and the weight loss in the studies behind it came from dieting and bariatric surgery rather than from tirzepatide.

The mechanism is the weight loss rather than the medicine, so it should carry across, but it has not been measured on Mounjaro specifically.

Mounjaro routinely produces more than 5% to 10% of body weight loss, and that is the range where ovulation starts to return.

So the question is not whether your fertility might change. It is whether your contraception will hold up if it does.

That matters most if your cycles have been irregular for years.

If you had come to assume you were not very fertile, and your periods turn regular a few months into treatment, your actual risk of pregnancy has changed even though nothing about your contraception has.

So a returning cycle is two things at once.

It is good news about your health, and it is a reason to check that your contraception is something you can rely on.

Mounjaro is not a fertility treatment and is not licensed as one.

But improved fertility is a predictable consequence of substantial weight loss, and it is better to plan ahead for it.

Mounjaro must not be used during pregnancy.

There is not enough human safety data to know whether it could harm a developing baby.

If you want to try for a baby, there is a gap to leave between your last injection and trying to conceive. The MHRA sets these out clearly:

Two things are worth noting here.

You need contraception through the washout period, not only while you are still injecting.

The gap exists because tirzepatide is still leaving your system, and your fertility may already have improved by the time it has gone.

And weight regain is common after stopping, which is worth discussing with your prescriber as part of planning rather than discovering afterwards.

If you have had unprotected sex, or you realise you have been in a four-week window without backup, act on it.

Be straight with whoever you speak to about the fact you are taking Mounjaro, because it changes what they will recommend.

Three things are worth knowing.

The copper coil is the most effective emergency option, and neither slowed absorption nor sickness affects it.

It does not need to be absorbed from your stomach, so slowed stomach emptying, vomiting, and diarrhoea are all irrelevant to it.

It can be fitted up to five days after unprotected sex. If you can access one in time, it is the strongest choice.

We do not know how well oral emergency contraception works alongside a GLP-1 medicine.

The FSRH says this openly: the effect has not been studied. It has not been shown to fail. It has simply not been measured.

Weight already affects oral emergency contraception, separately from Mounjaro.

FSRH guidance advises considering a double 3mg dose of levonorgestrel for anyone over 70kg or with a BMI above 26, and ulipristal (EllaOne) may be the better option closer to ovulation.

One caution: Ulipristal is less effective if you have taken a progestogen in the previous seven days, which includes the mini pill and most combined pills.

Not a crisis list. A tidy-up list.

1. Work out which window you are in. Find the date of your first injection, and the date of your most recent dose increase. If either is less than four weeks ago, you are in a window now.
2. Use condoms until that window closes. If you have already had unprotected sex during a window, read the emergency contraception section above rather than waiting to see what happens. Use a condom until that window closes.
3. Decide whether you want to keep tracking windows or switch method. Both are legitimate. Switching requires less effort. Staying on the pill is less change. There is no medically superior answer, only the one you are comfortable following.
4. Note down every future dose increase with a four-week reminder attached.
5. Raise it at your next consultation, even if you think you have it covered. It takes a minute, and prevention is always better than cure.

Talk about these five things at your consultation:

• The exact contraception you use, by name, including whether it is a combined pill or a mini pill
• Whether your periods are regular, and whether that has changed recently
• Whether you have PMOS or have ever been told you may have difficulty conceiving
• Whether you might want to try for a baby in the next year
• Any history of being sick or having diarrhoea on medication

Our consultation is straightforward. You fill in a short medical questionnaire, which takes 5 to 10 minutes and includes what contraception you use.

A GMC-registered prescriber reviews your answers and messages you through your account if anything needs discussing.

If treatment is suitable it is dispensed and dispatched for next-day delivery, in temperature-controlled packaging, with the needles and sharps bin included.

If it is not suitable, the prescriber tells you why, and you are not charged for treatment that is not issued.