Does GLP-1 Affect Hormones? A UK Guide (October 2026)

01 · The core answer

What GLP-1 medicines do to your hormones

GLP-1 medicines affect the hormones that govern hunger, fullness and blood sugar. That is the treatment mechanism. Mounjaro is the brand name for tirzepatide, a once-weekly injectable prescription medicine made by Eli Lilly.¹ It is licensed in the UK for weight management in adults and for type 2 diabetes.¹

One question is whether the medicine acts on the body's gut and metabolic hormones. It does, by design. The other is whether it changes sex hormones, menstrual hormones or menopause symptoms. Changes to sex hormones, menstrual hormones or menopause symptoms are not listed as side effects in the UK patient leaflet, so speak to your prescriber if this concerns you.

02 · Is this relevant to you?

Is this relevant to you, and what should you do next?

It is relevant if you already manage a hormone-related condition, take hormone therapy, or are considering treatment because of weight changes you link to hormones. The practical step is to be specific with the prescriber reviewing your consultation. Mention any thyroid condition, PCOS, menopause or perimenopause symptoms, hormonal contraception or HRT, and any plans for pregnancy.

Our free online consultation is reviewed by a GPhC-registered prescriber, who can weigh up your individual circumstances. If you want to see how treatment works in practice, our weight loss clinic explains the options, and the Mounjaro pen page shows current doses and prices.

03 · How the mechanism works

How GLP-1 and GIP hormones are involved

GLP-1 stands for glucagon-like peptide-1, a hormone made naturally in the gut. Medicines in this class copy or strengthen its signal. Mounjaro goes a step further. Tirzepatide is the first treatment of its kind to activate two natural gut-hormone receptors at once: GIP and GLP-1.¹

Together these help regulate appetite, slow how quickly the stomach empties, and improve the way the body responds to insulin.¹ In practice, most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.¹

This dual action is what distinguishes Mounjaro from single-action GLP-1 medicines such as semaglutide (Wegovy/Ozempic).¹ If you are weighing the two, our Wegovy pen page sets out that option too.

04 · Insulin and blood sugar

Insulin response and blood sugar

The medicine improves the way the body responds to insulin.¹ This is why tirzepatide is licensed for type 2 diabetes as well as weight management.¹

If you take other diabetes medicines, especially insulin or sulfonylureas, the doses may need adjusting because of the risk of low blood sugar. This is a conversation for your prescriber, not something to change yourself. Do not stop or alter any diabetes medicine on your own because you have read about hormones online.

05 · Sex hormones and menopause

Oestrogen, testosterone, PCOS and menopause

The most honest position is a plain one: effects on sex hormones are not established effects of the medicine. Mounjaro is not licensed to treat menopause symptoms, PCOS or low testosterone.

If menopause symptoms are your main concern, your GP or a menopause specialist is the right first contact, and hormone replacement therapy is a separate decision with its own risks and benefits.

If you are on HRT and considering Mounjaro, tell the prescriber reviewing your consultation. They can look at your full medicine list. Do not stop HRT to start weight-loss treatment without advice.

If you notice a new symptom after starting treatment, discuss it with your prescriber. You can also report it through the Yellow Card scheme.¹⁹

06 · Periods, fertility, mood

Periods, pregnancy, fertility and mood

• For menstrual changes, see our guide on whether GLP-1 affects your period.
• For pregnancy planning and safety, read about GLP-1 and pregnancy. Mounjaro must not be used during pregnancy, and it should be stopped at least one month before trying to conceive. If you become pregnant during treatment, stop the medicine and tell your prescriber promptly.
• If fertility is your concern, see whether GLP-1 can affect fertility.
• For feelings and wellbeing, our page on GLP-1 and mood covers what is known.

The medicine slows how quickly the stomach empties.¹ That is relevant to anything taken by mouth. Mounjaro slows stomach emptying, which can reduce how well oral contraceptive pills are absorbed. The SmPC advises switching to a non-oral method, or adding a barrier method (such as condoms), for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase. Ask your prescriber how your other oral medicines fit with treatment.

07 · Mounjaro specifically

Does Mounjaro affect hormones differently?

Mounjaro acts on GIP as well as GLP-1, so it touches a broader set of gut-hormone signals than single-action medicines.¹ That does not mean it has wider effects on sex hormones.

We have a dedicated page on whether Mounjaro affects hormones, and another on how GLP-1 medicines affect hormones in general terms. For the more worried version of the question, see whether GLP-1 messes with your hormones.

When treatment stops, the medicine clears slowly. Tirzepatide takes roughly four to five weeks to clear the system, there is no way to speed this up, and nothing needs doing while it clears.¹

08 · Results and expectations

What the weight results mean for hormone-related weight gain

If hormonal weight gain is your reason for asking, the clearest evidence is on overall weight. In the SURMOUNT-1 trial of 2,539 adults, people taking tirzepatide alongside diet and exercise lost on average 15% of their body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, compared with 3.1% with lifestyle changes alone.²

These are trial averages. Individual results vary, and treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them.²

09 · Who can get it

Who can have treatment, on the NHS or privately

Mounjaro is available on the NHS, but access is being phased in over several years. NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition, and the NHS primary-care rollout began in June 2025 with the highest-need groups first (initially BMI 40+ with four or more qualifying conditions).⁴⁶ Full rollout is expected to take years, which is why many people who meet the licensed criteria choose regulated private treatment rather than waiting.

Privately, our Mounjaro is supplied through official LillyDirect supply, sourced directly from Eli Lilly, after a free consultation reviewed by a GPhC-registered prescriber.

Mounjaro is a prescription-only medicine, used alongside a reduced-calorie diet and increased physical activity. Serious side effects are uncommon but need urgent attention. Seek immediate medical help for severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. Individual results vary. This page is information, not a substitute for medical advice.¹