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Is Mounjaro Making Your Birth Control Fail?

Checked on 8 sources5 min read
Short answer

It might, and the maker put it in writing. Mounjaro's patient leaflet says: "Birth control pills by mouth may not work as well while using MOUNJARO." In the study the label prints, the pill's hormones peaked at less than half their usual level after one dose. The leaflet adds: "It is not known if MOUNJARO will harm your unborn baby."

  • 34 of 100 what was left of the peak
  • 66 of 100 missing from the peak
The peak level in the blood of one hormone from the pill, norgestimate, drawn as 100 beads. After one dose of Mounjaro it peaked 66% lower. The other two peaked 59% and 55% lower. Source: Mounjaro label, Eli Lilly, revised August 2026 [1].

We looked for a study that counts the pregnancies. As of October 2026, we found none.

Sources: the Mounjaro prescribing information and patient leaflet, both by Eli Lilly, both revised August 2026. Checked 10 October 2026. How we check.

The short version

  • After a single dose of Mounjaro, the pill's hormones peaked 55 to 66 percent lower.
  • The label names two risk windows: the four weeks after starting, and the four weeks after every increase.
  • If the pill fails, the label's first page says the drug "may cause fetal harm", based on animal studies.
  • The warning is on Mounjaro and Zepbound. Ozempic and Wegovy carry no such warning.
  • No study we found counts the pregnancies behind the warning.

Does Mounjaro affect birth control pills?

The Mounjaro label says birth control pills may not work as well, and it says so twice. The patient leaflet carries the warning, and the longer text for prescribers gives the reason and the fix. [1][2]

The patient leaflet
"Birth control pills by mouth may not work as well while using MOUNJARO."
The reason given
"Use of MOUNJARO may reduce the efficacy of oral hormonal contraceptives due to delayed gastric emptying."
What prescribers are told to advise
"switch to a non-oral contraceptive method or add a barrier method"
For how long
"for 4 weeks after initiation and for 4 weeks after each dose escalation"

A barrier method is one like a condom.

The four weeks start again with every increase. Someone who is still stepping up is back inside a risk window each time.

The warning is a few lines in a leaflet. Whether anyone says them out loud is another matter.

How much does Mounjaro lower the pill's hormones?

After one dose of Mounjaro, the pill's hormones peaked 55 to 66 percent lower. About a fifth less reached the blood in total. The label blames the stomach: the drug slows it down, so a swallowed pill sits there longer. [1]

The figures come from a label study of a combined pill and one dose of tirzepatide, the drug in Mounjaro.

Ethinyl estradiol
Peak level in the blood
59% lower
Total absorbed
20% lower
Norgestimate
Peak level in the blood
66% lower
Total absorbed
21% lower
Norelgestromin
Peak level in the blood
55% lower
Total absorbed
23% lower

The peak also arrived 2.5 to 4.5 hours late.

The UK's contraception faculty puts that study at 40 women, and every number in it comes from one dose. The label says the stomach delay "is largest after the first dose and diminishes over time". It does not say who ran the study, and Lilly's name is on the label. [6]

What happens if you get pregnant on Mounjaro?

The Mounjaro label says the drug "may cause fetal harm", based on animal studies, and calls the human data "insufficient". The patient leaflet puts it in plainer words. [1][2]

The first page
"Pregnancy: Based on animal studies, may cause fetal harm."
In rats
"fetal growth reductions and fetal abnormalities occurred at clinical exposure"
In people
The data are "insufficient to evaluate for a drug-related risk"
The patient leaflet
"It is not known if MOUNJARO will harm your unborn baby."

Clinical exposure means drug levels in the range a person on the medicine has.

Zepbound is the same drug, under the brand name used for weight loss. Its label is blunter: "Weight loss offers no benefit to a pregnant patient and may cause fetal harm." It tells prescribers to advise stopping the drug "when a pregnancy is recognized". [3]

So the leaflet carries two warnings at once. The pill may not work as well, and it is not known whether the drug harms an unborn baby.

Is the warning on Zepbound, Ozempic and Wegovy too?

The pill warning is on the Zepbound label, which is the same drug as Mounjaro. It is not on the Ozempic or Wegovy labels, which are semaglutide. [3][4][5]

Mounjaro
Drug
Tirzepatide
Pill warning on the label
Yes
Label revised
August 2026
Zepbound
Drug
Tirzepatide
Pill warning on the label
Yes
Label revised
August 2026
Ozempic
Drug
Semaglutide
Pill warning on the label
No
Label revised
May 2026
Wegovy
Drug
Semaglutide
Pill warning on the label
No
Label revised
June 2026

The Ozempic label reports its own pill study and found "No clinically relevant drug-drug interaction with semaglutide". A claim that every GLP-1 drug cancels the pill goes further than these four labels.

The UK faculty adds a second route in a statement that covers both drugs. It tells clinicians to "Follow missed pill rules if vomiting occurs within a few hours of pill taking". [6]

Does Mounjaro affect the implant, the IUD or the patch?

The Mounjaro label does not name them one by one. It says: "Hormonal contraceptives that are not administered orally should not be affected". [1]

"Should not" is the label's phrase, and the study it describes tested a pill. The UK regulator lists the implant and the coil, its word for an IUD, as non-oral methods. [7]

Do regulators outside the US give the same Mounjaro warning?

Regulators in the UK and Australia have put a version of the same warning in writing. It now stands on three continents. They differ on who is covered.

In the UK, the medicines regulator warned on 5 June 2025. It said Mounjaro "may reduce the effectiveness of oral contraceptives in those who are overweight". The US label has no weight condition. [7]

In Australia, the product information now carries the same two windows. The regulator's page says reduced effect "cannot be excluded". The regulator searched its side-effect database for pregnancy on the pill. It found one report for tirzepatide and one for semaglutide, and the page gives no detail on either. [8]

None of the three cites a study that counts pregnancies.

What nobody has shown

  • How many pregnancies there have been. We found no study that counts them.
  • What the hormone numbers look like after the first dose. The label prints none.
  • Whether other pills behave like the one tested. The study used one combined pill.
  • What the drug does to a human pregnancy. The label's word is "insufficient".

The other side

"May" is the label's own word. About four fifths of the pill's hormones still reached the blood, and the label says the delay fades with time.

Methods that are not swallowed "should not be affected", and Australia's database held a single report for tirzepatide.

The fetal findings come from animals. The label says they "coincided with" mothers that ate less and weighed less. It allows the drug in pregnancy "only if the potential benefit justifies the potential risk to the fetus".

A label warning shows a maker and a regulator being careful in writing. How often the pill fails, it cannot say.

What would change this

  • A study that follows pill users through their first months on tirzepatide and counts pregnancies.
  • Hormone numbers taken after several increases.

Three questions to ask next

The changelog

Ask better questions.

This label was revised in August 2026. When a line like this one changes, the Wednesday email says so.

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