More women who are on hormone replacement therapy (HRT) and using popular weight-loss injections like Mounjaro are being urged to speak with their doctors.
Experts worry that mixing these treatments could raise the risk of womb cancer due to how these medications interact inside the body.
How HRT Works and Why It Matters
HRT often involves giving women oestrogen to help ease menopausal symptoms like hot flushes, mood swings, and low libido.
But oestrogen can also thicken the lining of the womb, which might increase cancer risk.
To counter this, HRT usually includes progesterone or a synthetic form called progestogen. These keep the womb lining thin and safer.
Many women use oestrogen gels or skin patches, which are absorbed through the skin, but take progesterone as oral pills, which need to be absorbed through the stomach lining into the bloodstream.
Why Weight-Loss Injections Might Interfere
Drugs like Mounjaro, Ozempic, and Wegovy contain ingredients that slow down digestion, a process called “gastric emptying.”
This can cause nausea or vomiting but also affects how well pills are absorbed when taken by mouth.
New guidelines from the British Menopause Society (BMS) highlight that because of this slowed digestion, the absorption of oral progesterone might be reduced when taken alongside these weight-loss injections.
This could, in theory, raise the risk of womb cancer by letting the lining thicken unchecked.
Adjusting Treatment When Starting Mounjaro
Professor Annice Mukherjee, an endocrinologist who helped write the BMS guidelines, explains that the effect on progesterone absorption is strongest when someone first starts on Mounjaro.
Doctors are now being advised to consider increasing the dose of oral progestogen during this initial phase and each time the weight-loss drug dose goes up to balance things out.
These recommendations mainly apply to women who take oestrogen via gels or patches but rely on oral progestogen tablets.
Women on combined oral contraceptives or those who’ve had a hysterectomy (and only take oestrogen) are not part of these guidelines.
Why This Matters for Women with Obesity and Diabetes
Professor Mukherjee points out that women with obesity and diabetes—conditions these drugs aim to treat—already face higher risks of womb lining thickening and cancer.
For these women, transdermal oestrogen (patches or gels) is usually safer than oral oestrogen, which can increase blood clot risks.
Alternatives and Warning Signs
Dr. Alice Scott, a menopause specialist, suggests alternatives such as switching from oral progesterone to a non-oral form like the Mirena coil or using combined hormone patches.
She has also seen cases of unexpected bleeding and spotting linked to reduced progestogen absorption.
A major concern is women buying these weight-loss injections online without medical advice.
Dr. Scott warns that this can lead to missing out on important safety guidance, including how these drugs might affect other medications.
Oral Contraceptives and Unexpected Pregnancy Risks
These weight-loss drugs may also reduce how well oral contraceptive pills work, raising the risk of unplanned pregnancy.
It’s crucial for women using any of these medications to talk openly with their doctors to avoid surprises.
Unfortunately, many people don’t tell their doctors they’re using weight-loss shots, so healthcare providers are encouraged to ask directly during medication reviews.
What the Drug Makers Say
Novo Nordisk, maker of Ozempic and Wegovy, stresses these drugs should be taken under medical supervision.
They note there haven’t been specific trials looking at how their drugs interact with HRT but advise caution since the slowed digestion could affect absorption of oral meds.
Eli Lilly, which makes Mounjaro, similarly warns that their drug delays stomach emptying and can influence how oral medications are absorbed, especially when first starting treatment.
They advise patients to consult healthcare professionals for the best treatment plans and to report any side effects.