Overview
Mounjaro (tirzepatide) weight loss injections
Mounjaro is a once-weekly injectable treatment containing tirzepatide. It supports weight management by helping to reduce appetite, curb cravings, and keep you feeling fuller for longer.
For adults aged 18+ only. Treatment is supplied following clinical assessment and approval.
How Mounjaro works
Tirzepatide acts on two gut-hormone pathways (often described as “dual action”). This can help you feel satisfied with smaller portions and reduce the urge to snack. It may also slow stomach emptying, which can contribute to feeling full for longer.
Who may be eligible?
Mounjaro may be considered for adults who meet one of the following:
- BMI 30+, or
- BMI 27+ with a weight-related health condition (e.g. raised blood pressure, high cholesterol, pre-diabetes, or sleep apnoea).
Eligibility is confirmed during the OnlineUKPharmacy medical questionnaire and clinician review.
Available strengths
- 2.5mg (starter dose)
- 5mg
- 7.5mg
- 10mg
- 12.5mg
- 15mg (maximum strength)
Your clinician will advise the most appropriate dose and when (or if) to increase.
How often is it taken?
Mounjaro is taken once weekly, ideally on the same day each week. If you need to change your dosing day, follow the guidance from your prescriber and the patient leaflet.
Where to inject
Common injection sites include:
- Abdomen (stomach)
- Thigh
- Upper arm
Rotate sites to help reduce irritation and avoid injecting into sore or damaged skin.
Dose escalation overview
Many patients begin with a lower starter dose and then step up gradually to improve tolerability. A common approach is shown below (your plan may differ depending on side effects and clinical advice):
| Time on treatment | Typical dose | Notes |
|---|---|---|
| Weeks 1–4 | 2.5mg once weekly | Starter phase to help your body adjust. |
| Weeks 5–8 | 5mg once weekly | Step-up if tolerated and clinically appropriate. |
| Ongoing | 7.5mg → 10mg → 12.5mg → 15mg | Further increases are made gradually when suitable. |
Side effects and important safety information
Very common / common side effects
- Nausea, vomiting, diarrhoea, constipation, tummy pain
- Indigestion or reflux symptoms
- Reduced appetite, tiredness, dizziness
- Injection-site redness, itching, or irritation
Contraception note
Tirzepatide can affect absorption of oral contraceptive pills, particularly when starting treatment and after dose increases. If you use the pill, consider an additional barrier method for a period after starting and after each dose increase, and seek medical advice about the most suitable contraception while using Mounjaro.
This page is not a substitute for the manufacturer’s leaflet. Always read the patient information leaflet supplied with your medication.
Storage
- Store unopened pens in the fridge (2°C to 8°C) and keep in the original packaging.
- Do not freeze. If a pen has been frozen, it should not be used.
- After first use, the pen may be kept at room temperature (up to 30°C) for a limited time, or stored in the fridge between doses.
- Keep the cap on when not in use to protect from light.
How OnlineUKPharmacy supplies Mounjaro
- Complete a short online consultation to check suitability and eligibility.
- Clinical review by a qualified prescriber.
- Discreet delivery if approved, with ongoing support available during treatment.
What happens if I decide to stop taking Mounjaro?
When Mounjaro treatment is discontinued, its effects on appetite control and blood-glucose regulation gradually diminish. As a result, hunger levels may increase, making it easier to consume excess calories and potentially regain some of the weight lost during treatment. The amount of weight regained differs between individuals, but evidence suggests that maintaining weight loss becomes more difficult once treatment is stopped.
Data from the SURMOUNT-4 clinical trial (https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2841273) showed that participants who discontinued Mounjaro after 36 weeks were more likely to regain a portion of their lost weight. In addition, several important health indicators, including blood pressure and cholesterol levels, began to trend back towards their levels before treatment.
These results indicate that continuing Mounjaro as prescribed, alongside long-term dietary and lifestyle improvements, can help sustain weight loss and preserve the wider health benefits achieved during treatment.
Always seek guidance from your prescriber before stopping or making any changes to your medication.
Side Effects
What side effects can occur with Mounjaro?
Like all medicines, Mounjaro can cause side effects, but not everyone gets them. Some effects are mild and improve as your body adjusts, while a smaller number can be more serious and need urgent medical attention.
What are the serious side effects of Mounjaro?
Serious side effects are uncommon or rare, but it’s important to recognise them early.
Uncommon (up to 1 in 100 people)
- Acute pancreatitis (inflamed pancreas): severe, persistent abdominal pain that may spread to the back. Seek urgent medical help immediately if this happens.
Rare (up to 1 in 1,000 people)
- Severe allergic reaction (e.g. anaphylaxis or angioedema): breathing difficulties, swelling of the face/lips/tongue/throat, trouble swallowing, wheezing, fast heartbeat, pale/cold skin, feeling faint, dizzy, or very weak. Get emergency medical help immediately.
What are the very common side effects?
Very common side effects (more than 1 in 10 people) may include:
- Nausea
- Diarrhoea
- Vomiting
- Stomach (abdominal) pain
- Constipation
- Low blood sugar (hypoglycaemia) when tirzepatide is used for type 2 diabetes with a sulphonylurea and/or insulin
Symptoms of low blood sugar can include headache, drowsiness, weakness, dizziness, hunger, confusion, irritability, sweating, and a fast heartbeat. If you use insulin or a sulphonylurea, your prescriber may need to adjust your dose.
What are the common side effects?
Common side effects (up to 1 in 10 people) may include:
- Mild allergic reactions (e.g. rash, itching, eczema)
- Dizziness
- Low blood pressure
- Reduced appetite
- Indigestion (dyspepsia)
- Bloating
- Burping
- Wind (flatulence)
- Reflux / heartburn
- Hair thinning or hair loss
- Fatigue
- Injection-site reactions (e.g. redness, itching)
- Raised pancreatic enzymes on blood tests (e.g. lipase, amylase)
- Increased calcitonin levels on blood tests
- Gallstones
- Low blood sugar when used for type 2 diabetes with metformin plus an SGLT2 inhibitor
What are the uncommon side effects?
Uncommon side effects (up to 1 in 100 people) may include:
- Pain at the injection site
- Fast pulse / increased heart rate
- Gallbladder infection or inflammation (cholecystitis)
- Changes in taste
- Altered skin sensation (e.g. tingling)
- Slower stomach emptying
- Low blood sugar when used for type 2 diabetes with metformin alone
When should I seek medical advice?
Contact a healthcare professional if side effects are severe, persistent, or worrying. Seek urgent medical help immediately if you develop symptoms of pancreatitis or a severe allergic reaction.
When should I take Mounjaro?
Mounjaro is administered once weekly, ideally on the same day each week, in line with the prescribed dose-increase schedule provided by your clinician.
FAQs
Is Mounjaro the same as Wegovy?
No. Mounjaro and Wegovy are both injectable treatments used for weight management, but they contain different active ingredients and work in different ways.
Wegovy contains semaglutide, which mimics a naturally occurring hormone called GLP-1. This helps regulate appetite, slows stomach emptying, and can improve insulin sensitivity.
Mounjaro contains tirzepatide, which acts on GLP-1 and also mimics another hormone known as GIP. This “dual action” can further support appetite control and metabolic regulation.
Can I switch from Mounjaro to Wegovy?
In many cases, yes—but switching should be guided by a prescriber to make sure it is safe and appropriate for you.
It is commonly recommended to leave at least 1 week after your final Mounjaro injection before starting Wegovy. This “washout” period allows tirzepatide to reduce in your system and helps lower the risk of overlapping side effects.
When starting Wegovy, treatment typically begins at the starting dose (0.25mg), even if you were taking a higher strength of Mounjaro. This helps reduce side effects and allows your body to adjust to semaglutide.
What’s the difference between Mounjaro and Orlistat?
Orlistat is an oral medicine that reduces the absorption of dietary fat, which can lower overall calorie intake.
Mounjaro is a weekly injection that works differently—helping to regulate appetite and support blood-glucose control, while also slowing stomach emptying so you may feel fuller for longer.
What’s the difference between Mounjaro and Zepbound?
Mounjaro and Zepbound both contain tirzepatide and act in the same way.
Zepbound is the name used in the United States, while Mounjaro is the licensed brand name used in the UK.
Can I use Mounjaro while taking oral contraceptives?
Mounjaro may reduce the effectiveness of oral contraceptive pills, particularly during the first 4 weeks of treatment and for 4 weeks after any dose increase. This is because tirzepatide can slow stomach emptying, which may affect how the pill is absorbed.
If you use the combined pill or the progestogen-only pill, consider using an additional barrier method (such as condoms) for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase. You may also wish to discuss a non-oral or long-acting option (for example, an IUD) with a healthcare professional.
Vomiting and diarrhoea can also reduce pill effectiveness. If you vomit within 3 hours of taking the pill, or if you have severe diarrhoea lasting more than 24 hours, follow the “missed pill” guidance in your contraceptive leaflet and consider alternative protection if symptoms continue.
Can Mounjaro affect the menstrual cycle?
Weight loss can affect hormone balance in some people. Because body fat contributes to oestrogen production, changes in body weight may lead to changes in menstrual cycles for some women.
If you notice unexpected changes to your periods while using Mounjaro, seek advice from a healthcare professional.
Can Mounjaro be used during pregnancy?
Mounjaro is not recommended during pregnancy because there is limited information about its safety in pregnancy and potential effects on fetal development.
If you are pregnant, planning a pregnancy, or become pregnant while using Mounjaro, contact your doctor or prescriber promptly for advice.
Where can I buy Mounjaro in the UK?
Mounjaro is a prescription-only medicine in the UK and can only be supplied following assessment by a qualified prescriber.
With OnlineUKPharmacy, you can request treatment by completing an online consultation. A prescriber will review your answers to confirm suitability. If approved, the medication can be supplied with discreet delivery and ongoing support.
How do I store Mounjaro?
Before first use, store Mounjaro in a fridge between 2°C and 8°C, in the original packaging, protected from light. Do not freeze.
After first use, the pen may be kept at room temperature (up to 30°C) for a limited period, or returned to the fridge between doses. Keep the cap on when not in use to protect it from light.
Can I buy Mounjaro over the counter?
No. Mounjaro cannot be purchased over the counter in the UK. It must be prescribed following a clinical assessment.
If you are unsure whether Mounjaro is suitable for you, complete the OnlineUKPharmacy consultation so a prescriber can review your eligibility.
