In your first month on Mounjaro you take the 2.5mg starter dose once a week by self-injection. This dose is designed to let your body adjust, not to drive maximum weight loss, so expect reduced appetite, possible nausea or digestive upset, and only modest early weight change. Most people stay on 2.5mg for the whole first four weeks before any dose increase.
What dose of Mounjaro do you take in the first month?
In the first month of Mounjaro you take the 2.5mg starter dose, injected once a week on the same day each week. Mounjaro (tirzepatide) is a prescription-only medicine that activates two gut-hormone receptors — GLP-1 and GIP — at the same time to reduce appetite.
The 2.5mg dose is a starting dose, not a treatment dose. It eases your body into the medicine to limit side effects. Only after at least four weeks will a prescriber consider moving you up to 5mg, then onwards through 7.5mg, 10mg, 12.5mg and a maximum licensed dose of 15mg if clinically appropriate.
When does Mounjaro start working in the first month?
Most people notice appetite changes within the first one to two weeks on Mounjaro, often before the scales move much. You may feel full sooner at meals, think about food less between meals, and finish smaller portions without effort.
Early weight change in the first month is usually modest and varies from person to person. The larger average results seen in trials came from the top dose over many months, not from the 2.5mg starter dose. 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.
What side effects are common in the first month?
The most common Mounjaro side effects, affecting more than 1 in 10 people, are nausea, diarrhoea, constipation, vomiting, decreased appetite and fatigue. These tend to be most noticeable in the days after each injection and often settle as your body adjusts over the first few weeks.
Side effects happen largely because Mounjaro slows how quickly your stomach empties and changes appetite signalling. Practical steps that help in the first month include:
- Eat smaller portions and stop when you feel full rather than finishing out of habit.
- Choose plainer, lower-fat meals on injection day if nausea is an issue.
- Stay hydrated, especially if you have diarrhoea or vomiting.
- Increase fibre and fluids to help with constipation.
- Avoid large, rich or greasy meals, which can worsen nausea.
Serious but rare risks include severe allergic reaction, acute pancreatitis, severe hypoglycaemia (low blood sugar), severe gastrointestinal disease and worsening diabetic retinopathy. Seek urgent medical help for severe or persistent abdominal pain, a severe allergic reaction, or symptoms that concern you. You can report suspected side effects to the MHRA via the Yellow Card scheme at https://yellowcard.mhra.gov.uk/.
How do you inject Mounjaro in the first week?
Mounjaro is a once-weekly injection you give yourself under the skin of your abdomen, thigh or upper arm. In the first week you pick a day that suits your routine and keep that as your weekly injection day.
- Choose and note your weekly injection day — consistency matters more than the exact day.
- Rotate the injection site each week to avoid irritation.
- Follow the device instructions supplied with your pen and the guidance from your prescriber.
- Store the medicine as directed on the patient information leaflet.
If you miss a dose, follow the advice in your patient information leaflet and contact your prescriber if you are unsure. Never take extra to catch up.
What should you eat and do in the first month?
Mounjaro works best alongside lifestyle changes, so the first month is a good time to build steady habits rather than restrict drastically. Because your appetite will likely fall, the priority is making the food you do eat count.
- Prioritise protein to help protect muscle while you lose weight.
- Include vegetables, fruit and fibre to support digestion.
- Eat regular, smaller meals rather than skipping and then overeating.
- Drink plenty of water across the day.
- Add gentle, regular movement such as walking.
Alcohol can add empty calories and may worsen nausea or digestive upset, so many people choose to limit it early on.
What are the Mounjaro doses and monthly prices?
Mounjaro is titrated gradually from the 2.5mg starter dose up to a maximum of 15mg. The monthly price depends on the dose you are prescribed:
| Dose | Price per month |
|---|---|
| 2.5mg (starter) | £160 |
| 5mg | £185 |
| 7.5mg | £240 |
| 10mg | £260 |
| 12.5mg | £275 |
| 15mg | £295 |
You can read more on the Mounjaro page, compare it with the Wegovy injection, the Wegovy Tablet and Foundayo, or see the full treatments overview.
Who is Mounjaro suitable for?
Mounjaro may be suitable for adults aged 18 or over with a BMI of 30 or more, or a BMI of 27 to 30 with a weight-related condition such as type 2 diabetes, high blood pressure or sleep apnoea. It is a prescription-only medicine, so it is only supplied if a GPhC-registered prescriber decides it is clinically appropriate after an online consultation.
Mounjaro is not suitable if you are pregnant, planning pregnancy or breastfeeding; have type 1 diabetes; have a personal or family history of medullary thyroid carcinoma or MEN2; have a history of pancreatitis; have severe gastrointestinal disease; have an active eating disorder; have severe liver or kidney impairment; or are allergic to the active ingredient.
You can check your eligibility through a free online consultation. A prescription is only issued if clinically appropriate — treatment is never guaranteed — and you receive ongoing prescriber support throughout.
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.
