Are Mounjaro and Wegovy the same?
No, Mounjaro and Wegovy are not the same medicine. Mounjaro contains tirzepatide. The UK patient leaflet describes Mounjaro as a medicine used for type 2 diabetes and also for weight loss and weight maintenance in adults who meet BMI and weight-related health criteria. It works mainly by helping regulate appetite, fullness, hunger and food cravings. [1]
Wegovy contains semaglutide. The UK patient leaflet describes Wegovy as a medicine for weight loss and weight maintenance that is similar to the natural GLP-1 hormone and acts on appetite receptors in the brain. [3]
The practical difference is not just the brand name. The active ingredient, receptor activity, dose schedule, side-effect profile, product information and evidence base are different. That is why the two medicines should not be treated as interchangeable, even though both can be used for weight management under medical supervision.
Mounjaro vs Wegovy at a glance
|
Question
|
Mounjaro
|
Wegovy
|
What it means
|
|
Active ingredient
|
Tirzepatide
|
Semaglutide
|
This is the key factual correction: Mounjaro is not a semaglutide medicine.
|
|
Medicine type
|
GIP and GLP-1 receptor agonist
|
GLP-1 receptor agonist
|
Both affect appetite signals, but the receptor activity is different.
|
|
How often it is used
|
Once weekly injection under the skin
|
Once weekly injection under the skin
|
The weekly routine is similar, but the dosing steps are not equivalent.
|
|
Adult weight-management eligibility in product information
|
BMI 30 or above, or BMI at least 27 with weight-related health problems, alongside reduced-calorie diet and increased physical activity. [1]
|
BMI 30 or above, or BMI 27 to under 30 with weight-related health problems, alongside diet and physical activity. [3]
|
A prescriber still needs to assess suitability, contraindications and risk.
|
|
Typical adult dose escalation
|
Starts at 2.5mg once weekly for four weeks, then 5mg; may increase by 2.5mg steps up to 15mg if needed. [2]
|
Starts at 0.25mg once weekly and usually increases every four weeks to 2.4mg; UK product information also includes a 7.2mg option for some adult patients with obesity if needed. [4]
|
The milligram numbers cannot be converted directly between medicines.
|
|
Weight-loss evidence
|
Head-to-head trial evidence favoured tirzepatide for average weight loss at 72 weeks. [5]
|
Established weight-management evidence and NICE guidance for semaglutide. [7]
|
Trial averages help frame expectations but do not predict individual response.
|
|
Main tolerability issue
|
Gastrointestinal side effects are common, especially during escalation. [2]
|
Gastrointestinal side effects are common, especially during escalation. [4]
|
Side effects, dehydration risk and personal medical history can affect the choice.
|
Which works better for weight loss?
For average weight loss in the most direct comparison currently available, tirzepatide performed better than semaglutide. In SURMOUNT-5, a phase 3b head-to-head trial, adults with obesity but without type 2 diabetes received the maximum tolerated dose of tirzepatide, either 10mg or 15mg, or semaglutide, either 1.7mg or 2.4mg, once weekly for 72 weeks. The average percentage weight change was -20.2% with tirzepatide and -13.7% with semaglutide. [5]
That is useful evidence, but it needs to be interpreted properly. It does not mean every individual will lose more weight on Mounjaro. It also does not remove the need to consider side effects, tolerability, previous response, diabetes medicines, pregnancy plans, eye disease, digestive problems, access and clinical judgement.
A more useful question than 'which is better?' is: which medicine is clinically suitable, tolerable and sustainable for this patient at this stage?
Why Mounjaro and Wegovy doses are not equivalent
Mounjaro and Wegovy doses should not be compared by milligrams. A 5mg dose of one medicine is not equivalent to a 5mg dose of the other because tirzepatide and semaglutide are different molecules with different receptor activity and different product information.
Mounjaro usually starts at 2.5mg once weekly for four weeks, then increases to 5mg once weekly. If needed, a prescriber may increase by 2.5mg steps to 7.5mg, 10mg, 12.5mg or 15mg once weekly, with at least four weeks on a dose before moving higher. [2]
Wegovy usually starts at 0.25mg once weekly and increases every four weeks through 0.5mg, 1mg and 1.7mg to 2.4mg once weekly. Current UK product information also includes a 7.2mg once-weekly option for some adult patients with obesity if needed, using three 2.4mg injections on the same day under prescriber direction. [4]
Do not use online dose-conversion charts to switch between Mounjaro and Wegovy. Do not overlap them, combine them or restart at a high dose after a break unless your prescriber has told you to do so.
Side effects and safety: what to watch for
Both medicines can cause side effects. The most common issues are gastrointestinal: nausea, vomiting, diarrhoea, constipation, abdominal pain, indigestion, bloating or reflux. These effects are often more noticeable when starting or increasing a dose, but they should not be ignored if they are severe, persistent or causing dehydration. [2,4]
The key safety point is not simply whether side effects are 'worse' on one medicine. The important question is whether your symptoms fit an expected pattern, whether they are settling, and whether they could indicate a more serious problem.
|
Symptom or situation
|
Why it matters
|
What to do
|
|
Severe, persistent stomach or abdominal pain, with or without nausea, vomiting or pain through to the back
|
This can be a sign of acute pancreatitis, which both product leaflets describe as serious and potentially life-threatening.
|
Stop using the medicine and seek urgent medical help. [2,4]
|
|
Swelling of the face, lips, tongue or throat, difficulty swallowing, breathing problems, wheezing, fast heartbeat, dizziness or weakness
|
These can be signs of a severe allergic reaction.
|
Seek immediate medical help. [2,4]
|
|
Repeated vomiting, diarrhoea, inability to keep fluids down, dizziness, very dark urine or signs of dehydration
|
Fluid loss can lead to dehydration and may affect kidney function, especially if you already have kidney problems.
|
Contact a clinician promptly. Use urgent care if symptoms are severe or you feel very unwell. [1,3]
|
|
New or worsening vision problems, especially if you have diabetes
|
Fast changes in blood sugar control can affect diabetic eye disease. Wegovy product information also warns about sudden or worsening eyesight changes and rare NAION.
|
Contact your doctor urgently. Sudden or rapidly worsening eyesight needs urgent assessment. [3,4]
|
|
Cold sweat, fast heartbeat, confusion, weakness, hunger, shaking or feeling faint if you use insulin or a sulphonylurea
|
The risk of low blood sugar can increase when these medicines are used with some diabetes medicines.
|
Follow your diabetes plan and contact your prescriber. Your diabetes medicine dose may need review. [1,3]
|
|
Pregnancy, suspected pregnancy, breastfeeding or plans to conceive
|
These medicines are not suitable in pregnancy, and contraception advice differs between medicines.
|
Speak to your prescriber before starting, continuing or stopping treatment. Mounjaro may require additional contraception after starting and dose increases; Wegovy should be stopped before planned pregnancy as advised in product information. [1,4]
|
|
Upcoming operation or anaesthetic
|
Both medicines can slow stomach emptying, which matters for anaesthesia and aspiration risk.
|
Tell your doctor, surgeon or anaesthetist that you are taking Mounjaro or Wegovy. [1,3]
|
Can you switch from Wegovy to Mounjaro, or from Mounjaro to Wegovy?
Some patients may switch from Wegovy to Mounjaro, or from Mounjaro to Wegovy, but it should be a prescriber-managed decision. Switching may be considered because of side effects, response, supply, access, medical history or treatment goals. It should not be treated as a simple brand swap.
Before switching, a clinician should consider:
- your current medicine, current dose and how long you have been taking it;
- whether your side effects are mild, settling, persistent or clinically concerning;
- whether you have had pancreatitis, gallbladder problems, severe constipation, gastroparesis, kidney problems or eye disease;
- whether you take insulin, sulphonylureas, warfarin or other medicines needing closer monitoring;
- whether pregnancy, breastfeeding or contraception advice applies;
- whether there has been a treatment break, missed doses or incorrect dosing.
Do not combine Mounjaro and Wegovy. Wegovy product information says not to use it with other GLP-1 receptor agonists, and both medicines should be used exactly as prescribed. [3,4]
If you are switching provider as well as switching medicine, the clinical team should still know your full dose history, side effects, weight response, other medicines and relevant medical history. The safest switch is a documented clinical switch, not a self-managed one.
How to think about choosing between Mounjaro and Wegovy
The right medicine is not decided by a headline result alone.
A balanced decision should include:
-
Eligibility: whether your BMI, weight-related health conditions and medical history fit the medicine's licensed use and the provider's clinical criteria.
-
Expected benefit: what level of weight loss is realistic for your starting point, treatment stage and dose.
-
Tolerability: whether nausea, constipation, reflux, vomiting or other side effects are manageable and improving.
-
Risk factors: pancreatitis history, diabetic eye disease, severe digestive problems, kidney issues, gallbladder symptoms, pregnancy plans or interacting medicines.
-
Monitoring: whether you need closer follow-up, especially if you have diabetes or are taking medicines that can cause low blood sugar.
-
Practicality: availability, continuity of supply, dose schedule, aftercare and whether you can follow the treatment plan safely.
Cost and availability matter in real life, but they should not override clinical suitability. A cheaper or more available medicine is not a good choice if it is unsafe for you, poorly tolerated or not appropriate for your medical history.
Where Ozempic fits into the comparison
Ozempic often appears in searches around Mounjaro and Wegovy because it also contains semaglutide. The important distinction is licensing and clinical use. Wegovy is semaglutide used for weight management under its product information. Ozempic is a semaglutide medicine used for type 2 diabetes, not a like-for-like Wegovy alternative for weight management.
For this reason, patients should not assume Ozempic, Wegovy and Mounjaro are interchangeable. Active ingredient, indication, dose, supply route and clinical suitability all matter.
