These days, weight-loss injections like Mounjaro are being hailed as miracle tools for fighting obesity.
But as more and more women turn to these jabs—often without a prescription—doctors are raising a red flag about how these drugs might quietly interfere with other medications, especially hormone replacement therapy (HRT).
And yes, it could potentially increase the risk of womb cancer if not handled properly.
Why Doctors Are Warning Women on HRT About Mounjaro
So here’s the deal: many women take HRT to ease the worst parts of menopause—think hot flushes, low mood, night sweats, and all the other fun stuff that comes with hormonal changes.
HRT replaces estrogen, but because estrogen can thicken the womb lining (which could raise the risk of womb cancer), it’s paired with a second hormone—progesterone or a synthetic version called progestogen.
Usually, women take estrogen as a gel or patch, but the progesterone part often comes in pill form, taken orally. And this is where Mounjaro enters the chat.
What’s the Link Between Mounjaro and Womb Cancer?
Mounjaro, and other similar drugs like Ozempic and Wegovy, slow down digestion—something known as delayed gastric emptying.
While this helps people feel full and eat less, it can also reduce how well your body absorbs other medications taken by mouth.
And that includes oral progestogen. If less of it is absorbed, the womb lining might not stay as thin as it should—which theoretically raises the risk of developing womb cancer over time.
The British Menopause Society (BMS) has now stepped in with new guidelines, urging doctors to carefully monitor women on HRT who also start using Mounjaro.
What Doctors Are Now Recommending
Professor Annice Mukherjee, a consultant endocrinologist who helped draft the BMS guidelines, explains that the biggest impact on medication absorption happens when women first start Mounjaro, or when their dose increases.
That means doctors may need to temporarily bump up the dose of oral progestogen to keep things balanced.
Alternatively, doctors might suggest skipping oral progesterone altogether and switching to options like the Mirena coil (which slowly releases progesterone directly into the womb) or using a combined estrogen-progestogen patch.
What If You’re Using Mounjaro Without a Prescription?
Here’s where it gets tricky—and risky.
Dr. Alice Scott, a menopause specialist in Essex, says she’s seen women show up at her clinic with unexpected spotting or bleeding.
Often, they’ve been using weight-loss injections they bought online without telling their GP.
That means no proper medical advice, no discussions about how it might mess with their HRT—and no one watching out for signs of a potential problem.
That lack of oversight is what’s really worrying doctors.
Women on the Pill Could Also Be at Risk
It’s not just HRT users who need to be cautious. Women on the oral contraceptive pill should also be aware that weight-loss jabs may reduce how well the pill works.
This could increase the risk of an unplanned pregnancy—another thing people might not expect from a drug that seems totally unrelated to birth control.
And again, if you’re not telling your doctor you’re using Mounjaro or similar drugs, they won’t know to warn you.
A Warning from the Drugmakers Themselves
Both Novo Nordisk (makers of Ozempic and Wegovy) and Eli Lilly (who make Mounjaro) acknowledge that their drugs delay gastric emptying, which could mess with how oral medications are absorbed.
While they say clinical trials haven’t shown major interactions with oral meds, they do admit that caution is necessary, especially during the early stages of treatment.
That’s when the delay in digestion—and therefore the effect on medication absorption—is strongest.
Their bottom line? Always consult your healthcare provider before mixing these drugs with other meds, especially ones you rely on daily.
So, What Should Women Do?
The takeaway here isn’t to panic—but to be informed. If you’re on HRT or the pill and thinking about (or already using) a weight-loss jab like Mounjaro, talk to your doctor. Don’t skip the conversation, even if you got your injection online.
And if you’re a healthcare provider, experts say it’s time to start asking your patients about these popular jabs during medication reviews.
Because the truth is, many women simply aren’t bringing it up—and that silence could come at a cost.