Does Mounjaro affect my HRT?

Only one part of it, as far as anyone knows: progestogen you swallow, such as Utrogestan. The jab slows your stomach, so less may be absorbed, mostly in the 4 weeks after starting and after each step up. Oestrogen gel, patches and spray, combined patches and a hormonal coil aren't expected to be affected. So if you're on a combined patch or a hormonal coil like Mirena, there's nothing to change.

Why progesterone is the part to check

Mounjaro slows how fast your stomach empties. That can change how well some tablets get absorbed, mostly when you start and after each step up. If you have a womb and take oestrogen, the progestogen is there to protect your womb lining. If less of it gets absorbed, the lining may not be fully protected, and over time it can thicken. That's also why some women notice unexpected bleeding.

Very little is known about this yet.The British Menopause Society (BMS) says there are no data on whether Mounjaro changes oral progestogen, bleeding patterns or womb risk. Its April 2025 advice for GPs is a precaution borrowed from the pill data. Women on the forums say their online prescriber never asked about HRT, and their GP had never heard of the advice. It's new, so take it with you.

The options if you swallow your progestogen

The BMS gives your HRT prescriber three options:

• A 52mg hormonal coil (like Mirena). It works directly in the womb, so the jab's effect on your stomach doesn't touch it, and it's contraception too. The BMS calls it likely the most complete option. Already have one fitted within 5 years? The BMS says no change is needed.
• A higher dose by mouth for 4 weeks after starting, and again after each increase, until your Mounjaro dose is stable. The BMS says there's no data on exactly how much higher, so this one rests on expert judgement.
• Another route that skips your stomach. With several dose changes ahead, the BMS says a non-oral progestogen is preferable throughout. Vaginal progesterone is unlikely to be affected, though it isn't licensed for HRT, so that one is your HRT prescriber's call.

On oestrogen tablets? The BMS suggests considering gel, patches or spray. Oestrogen through the skin doesn't raise your clot risk the way tablets do, which matters more when you're carrying extra weight, and the jab doesn't affect how it's absorbed.

If you start bleeding

Bleeding is the sign to watch, because it can mean the lining isn't getting the cover it needs.

• Spotting on HRT: tell your HRT prescriber, especially after starting the jab or a step up.
• Flooding or clots at any stage: contact your GP or menopause clinic this week.
• Any bleed after 12 months with no period, even a small one-off, needs your GP, promptly, every time. NHS advice is to get it checked. It's usually nothing serious, and it's always looked at. Don't put it down to the jab.

Can you start HRT while you're on the jab?

Yes. Nothing in the BMS advice says choose one or the other. It says choose your routes: oestrogen through the skin, and a progestogen route that sidesteps the absorption question. There may even be a bonus. In a 2026 Mayo Clinic study, women on HRT lost about 35% more weight on tirzepatide. It wasn't randomised, so it can't prove cause.

Ask your prescriber "I take my progestogen by mouth and I've started Mounjaro. Which BMS option do you want me on, and for how long?"