Mounjaro (tirzepatide) works by activating two natural gut-hormone receptors at once — GLP-1 and GIP. Together these reduce your appetite, slow how quickly your stomach empties and help you feel fuller for longer, so you naturally eat less and find it easier to keep to a calorie deficit alongside diet and lifestyle changes.
The short answer
When you eat, your gut releases hormones that tell your brain you are satisfied. Mounjaro mimics two of these hormones, amplifying those "I've had enough" signals for the whole week between injections.
The result is usually less hunger, smaller portions feeling filling, and fewer food cravings. This is why it is described as an appetite-based treatment rather than a "fat-burner" — it changes how much you want to eat, not your metabolism in a mysterious way.
What makes Mounjaro different: the dual mechanism
Most weight-management injections, such as the Wegovy injection, act on a single receptor (GLP-1). Mounjaro is a dual agonist — it targets GLP-1 and GIP.
GLP-1 (glucagon-like peptide-1)
Activating the GLP-1 receptor slows stomach emptying, dampens appetite signals in the brain and supports better blood-sugar control after meals. This is the effect you feel most as reduced hunger.
GIP (glucose-dependent insulinotropic polypeptide)
GIP is a second gut hormone involved in how the body handles fat and sugar. Adding GIP activity is thought to complement the GLP-1 effect on appetite and energy balance. The two working together is the key feature of tirzepatide.
What this feels like week to week
Because Mounjaro is a once-weekly self-injection, its effect is steady rather than a daily spike. Many people notice they feel full sooner, lose interest in second helpings, and think about food less.
It is not an appetite "off switch", and it does not do the work for you. The medicine makes healthier eating and portion control easier to sustain, which is why every clinical result is reported "alongside lifestyle support".
How Mounjaro is dosed
Mounjaro is started low and increased gradually. This titration gives your body time to adjust and helps limit side effects such as nausea.
- 2.5mg (starter dose)
- 5mg
- 7.5mg
- 10mg
- 12.5mg
- 15mg (maximum licensed dose)
You inject once a week, on the same day each week. A prescriber reviews your progress and tolerance before each step up — you should never increase the dose faster than advised.
| Dose | Price per month |
|---|---|
| 2.5mg | £160 |
| 5mg | £185 |
| 7.5mg | £240 |
| 10mg | £260 |
| 12.5mg | £275 |
| 15mg | £295 |
The cheapest starting dose is £160/month. You can see full details on the Mounjaro treatment page or compare options across our treatments overview.
How effective is it?
In the SURMOUNT-1 trial, participants on the 15mg dose lost on average 22.5% of body weight over 72 weeks, alongside lifestyle support. Individual results vary; not everyone reaches this.
That figure reflects the highest dose in a controlled trial with structured support. Your own results depend on your starting point, your dose, how your body responds and how consistently you combine the medicine with diet and activity.
Who Mounjaro is suitable for
Mounjaro is a prescription-only medicine for weight management in adults. You may be eligible if you are:
- Aged 18 or over, and
- Living with obesity (BMI 30 or above), or
- BMI 27–30 with a weight-related condition such as type 2 diabetes, high blood pressure or sleep apnoea.
It is not suitable if you are pregnant, planning pregnancy or breastfeeding; have type 1 diabetes; have a personal or family history of medullary thyroid cancer or MEN2; have a history of pancreatitis; have severe gastrointestinal, liver or kidney disease; have an active eating disorder; or are allergic to tirzepatide.
A treatment is only prescribed if it is clinically appropriate after a free online consultation with a GPhC-registered prescriber. A prescription is never guaranteed.
Side effects to be aware of
Because Mounjaro slows the gut and reduces appetite, the most common side effects are digestive and usually ease as your body adjusts.
Common (affecting more than 1 in 10 people):
- Nausea
- Diarrhoea
- Constipation
- Vomiting
- Decreased appetite
- Fatigue
Serious but rare risks include severe allergic reaction, acute pancreatitis, severe hypoglycaemia (low blood sugar), severe gastrointestinal disease and worsening diabetic retinopathy. Seek medical advice promptly if you experience severe or persistent symptoms, particularly severe abdominal pain.
You can report any suspected side effect to the MHRA via the Yellow Card scheme at https://yellowcard.mhra.gov.uk/.
How Mounjaro compares with other options
Mounjaro is the only dual GLP-1/GIP treatment we offer. If you prefer a tablet or a single-hormone injection, there are alternatives to discuss with a prescriber:
- Wegovy injection — a once-weekly GLP-1 receptor agonist.
- Wegovy Tablet — the same active medicine as the Wegovy injection, taken as a once-daily tablet on an empty stomach.
- See all weight-loss injections in one place.
No single medicine is "best" for everyone. The right choice depends on your health, preferences and how you respond — which is exactly what the clinical consultation is for.
Getting started
The process is straightforward: complete a free online consultation, a registered prescriber reviews your answers (with a short video consultation where clinically needed), and if suitable the medicine is dispensed by our UK pharmacy and sent by tracked delivery, with ongoing prescriber support.
Ready to check whether Mounjaro could be right for you? Start with our free eligibility check, or read more on the blog and about us pages.
This article is for information only and is not a substitute for personalised medical advice. Weight-loss medicines are prescription-only, are not suitable for everyone, and are prescribed only after a clinical consultation with a GPhC-registered prescriber. Individual results vary. Always speak to a UK-registered pharmacist or doctor before starting or changing any prescription medication.
