How does Mounjaro work?

Mounjaro is a prescription medicine that contains tirzepatide. People across the UK are searching for it because it can support weight loss by reducing appetite and helping you feel fuller for longer. This guide explains what it is, how it works, what to expect, and how to use it safely.

Medical disclaimer: This article is general information, not personal medical advice. Speak to a clinician or pharmacist about your situation.

What is Mounjaro?

Mounjaro is the brand name for tirzepatide. It has been used for type 2 diabetes and is also authorised in the UK for weight management and weight loss in adults who meet certain criteria.

It is a self injected medicine taken once weekly, used with a reduced calorie diet and increased physical activity.

NHS England says tirzepatide for weight management is prescribed through specialist weight management services with wider clinical support. 

How does Mounjaro work in the body?

It targets two hormone pathways (dual incretin effect)

After you eat, your gut releases hormones that help regulate hunger and blood sugar. Tirzepatide activates receptors for two pathways called GIP and GLP 1. This dual action is one reason it may feel different to medicines that mainly target GLP 1 alone.

It helps control appetite and cravings

Many people notice earlier fullness and smaller portions. Hunger signals can reduce, so sticking to planned meals may feel easier. Pair it with a reduced calorie plan and activity.

It slows stomach emptying

Tirzepatide can slow how quickly food leaves your stomach. This can help you feel full for longer. It can also explain nausea or a heavy full feeling, especially after large meals.

It improves blood sugar control

In type 2 diabetes, tirzepatide supports insulin release when needed and reduces signals that raise blood sugar. This can reduce glucose swings that can drive hunger for some people.

What results can people expect?

Appetite changes often come first. You may snack less and feel satisfied sooner.

Weight loss tends to be gradual across weeks and months. Results vary and consistency matters.

How long does Mounjaro take to work?

Some people feel appetite effects in the first few weeks. Weight change is often clearer after your dose increases gradually over time.

Doses are stepped up to reduce side effects. Follow your prescriber plan rather than rushing increases.

What are the most common side effects and why do they happen?

Digestive side effects

Common side effects are nausea, constipation or diarrhoea, indigestion, and reduced appetite. They are linked to appetite hormone effects and slower stomach emptying.

Tips to reduce side effects

• Eat smaller meals early on
• Limit high fat meals at the start
• Drink water regularly and build fibre gradually
• Choose protein first at meals
• Stick to the planned dose schedule

Seek clinical advice if you cannot keep fluids down or symptoms are severe.

Who should not use Mounjaro?

Do not use tirzepatide in pregnancy or while breastfeeding unless your specialist team advises it. Your prescriber will check your medical history and suitability.

Get urgent help for severe abdominal pain or signs of dehydration.

Avoid unregulated sources. The UK medicines regulator warns against buying weight loss medicines without a prescription, including via social media or beauty salons.

Mounjaro vs other injections (quick comparison)

Mounjaro targets both GIP and GLP 1 pathways. Some other weight management injections mainly target GLP 1. Choice should be clinician led, based on benefits, risks, and what is appropriate for your health.

How to use Mounjaro correctly

Use it on the same day each week and rotate injection sites based on your training. If you miss a dose, follow the patient information leaflet and prescriber advice. Store it as directed on the pack.

FAQs

Is Mounjaro insulin?

No. It is not insulin.

Do you gain weight back if you stop?

Weight can return if appetite increases again. Long term habits and follow up support reduce the risk.

Can I drink alcohol?

Alcohol adds calories and may worsen nausea for some people.

Do I need to diet while on it?

Yes. NICE and NHS guidance is that weight management medicines are used alongside a reduced calorie diet and increased physical activity.

Is it safe long term?

Your prescriber will review benefits and side effects regularly.

Does it affect contraception or other meds?

Ask a pharmacist to check your contraception and other medicines.

South Ealing Pharmacy weight loss service

South Ealing Pharmacy supports people in Ealing and online across the UK with clinician led weight loss consultations and ongoing reviews.

Private prices for Mounjaro at South Ealing Pharmacy (subject to clinical suitability and stock) are:

• 2.5mg £149
• 5mg £229
• 7.5mg £259
• 10mg £299
• 12.5mg £359
• 15mg £389

Key points and next step

• Mounjaro contains tirzepatide and is taken once weekly.
• It works by activating GIP and GLP 1 pathways to help you feel fuller and less hungry.
• Digestive side effects are common and often settle with time and simple changes.
• Best results come when medicine is paired with diet, activity, and ongoing review.

Book a weight loss consultation with South Ealing Pharmacy and discuss eligibility, side effects, and support.

Start your weight loss journey