Retatrutide vs Mounjaro: Which Is Better?

Retatrutide may produce greater average weight loss than Mounjaro based on clinical trial data so far, but it is too early to say it is better overall.

Mounjaro is already licensed and available in the UK for suitable patients. Retatrutide is still investigational, has not been approved by regulators and cannot legally be prescribed or supplied as a weight loss treatment.

The simplest answer is:

• Best current option: Mounjaro
• Most promising future option: Retatrutide
• Most weight loss in trial data so far: Retatrutide
• Most established safety profile: Mounjaro
• Available in the UK now: Mounjaro

The results should not be treated as a direct head-to-head comparison because they come from separate clinical trials.

The main difference between retatrutide and Mounjaro lies in how many metabolic hormones they target and how those hormones affect the body.

Mounjaro (tirzepatide) works by activating two hormones involved in appetite and blood sugar regulation:

• GLP-1: Helps reduce appetite and slows stomach emptying
• GIP: Enhances insulin release after eating and may help improve how the body processes nutrients and stores fat.

Retatrutide works on three hormones, which is why it is often referred to as a “triple-agonist.” It activates:

• GLP-1: Reduces appetite and slows digestion
• GIP: Improves insulin release and metabolic regulation
• Glucagon: Increases energy expenditure and may help the body burn more stored fat

The addition of glucagon is what makes retatrutide different. While glucagon normally raises blood sugar, in this context it also stimulates energy use and fat metabolism, which researchers believe may contribute to the greater weight loss seen in clinical trials so far.

Further reading: How retatrutide works

Retatrutide has shown greater average weight loss in trial data so far.

In the SURMOUNT-1 trial, Mounjaro helped people lose up to 22.5% of their starting body weight at 72 weeks.

Further reading: Mounjaro results

In the TRIUMPH-1 trial, retatrutide helped people lose 28.3% of their starting body weight at 80 weeks on the 12mg dose.

Further reading: Retatrutide results

These results are impressive, but they are not from a direct head-to-head trial. This means they should be compared cautiously.

Retatrutide may be stronger for weight loss based on trial results so far, but Mounjaro is currently the better treatment option for most eligible UK patients because it is approved and available.

A medicine is not judged only by weight loss. Other factors matter, including:

• whether it is licensed
• whether it is legally available
• how much safety data is available
• side effect risk
• long-term monitoring
• suitability for the patient
• cost and access
• clinical experience in real-world use

Retatrutide may become an important future treatment if it is approved, but Mounjaro is the current licensed option.

Mounjaro currently has the more established safety profile because it is licensed and already used in clinical practice.

Further reading: Is Mounjaro safe?

Retatrutide has been studied in clinical trials, but its full safety profile is still being assessed. Regulators have not yet completed their review, and it is not approved for routine use.

Further reading: Is retatrutide safe?

This means it is not accurate to say retatrutide is safer than Mounjaro. It is also not accurate to say it is unsafe based only on the fact that it is investigational. The more precise answer is that retatrutide’s safety is still being evaluated.

Both treatments can cause digestive side effects because they act on hormone pathways involved in appetite and digestion.

Common side effects may include:

• nausea
• diarrhoea
• constipation
• vomiting
• stomach discomfort
• reduced appetite

Mounjaro’s side effect profile is better established because it is licensed.

Retatrutide’s side effect profile is still being studied, although available trial data suggests digestive symptoms are common and can be dose-related.

For a full symptom-by-symptom breakdown, read our dedicated guides on Mounjaro side effects and retatrutide side effects.

Both Mounjaro and retatrutide affect hormone pathways involved in blood sugar control.

Mounjaro is already licensed for type 2 diabetes and is also authorised for weight management in suitable patients.

Retatrutide is being studied in people with type 2 diabetes, but it is not currently approved as a diabetes treatment.

At present, Mounjaro is the practical option for eligible patients who need a licensed treatment affecting both weight and blood sugar.

Retatrutide is not currently available in the UK as a licensed weight loss treatment.

It cannot legally be prescribed or supplied by UK pharmacies at the moment. It is still being studied in clinical trials.

If you see adverts or listings to buy retatrutide online, they should be avoided because the product may not be genuine, sterile, correctly dosed or legally supplied.

Mounjaro is available in the UK for suitable patients after a clinical assessment.

It may be prescribed for weight management in adults who meet the clinical criteria. Suitability depends on factors such as BMI, weight-related health conditions, medical history, current medication and safety considerations.

Mounjaro should be used alongside a reduced-calorie diet and increased physical activity.

If you are eligible for weight loss treatment now, Mounjaro may be the more practical option because it is licensed, available and supported by clinical guidance.

Retatrutide may become an important future treatment, but there is no guarantee of when it will become available, who it will be suitable for, or how it will be prescribed.

Waiting for retatrutide may delay treatment that is already available. If you are considering weight loss medication, it is better to have a clinical assessment and discuss licensed options now.

Not currently.

Retatrutide is not approved or available as a licensed treatment, so patients cannot switch from Mounjaro to retatrutide through a regulated UK pharmacy.

If retatrutide is approved in the future, switching guidance would need to come from official prescribing information and clinical assessment.

Mounjaro may be more suitable for patients who:

• want a licensed treatment available now
• meet the clinical criteria for weight management
• want a treatment with established prescribing guidance
• need a regulated medicine supplied through a UK pharmacy
• want ongoing clinical monitoring
• are not eligible for a retatrutide clinical trial

Suitability still depends on a full clinical assessment.

Retatrutide may be of interest in the future for patients who need greater weight loss or have obesity-related health conditions, if it is approved and judged suitable.

However, it is not currently a treatment option outside authorised clinical trials.

Until approval, it should be treated as a promising investigational medicine rather than an available alternative to Mounjaro.

Retatrutide has shown greater average weight loss than Mounjaro in separate clinical trials, but it is not currently approved or available.

Mounjaro is the better current option for eligible UK patients because it is licensed, available on prescription and has a more established safety profile.

Retatrutide may become a major future weight loss treatment if approved, but for now it should not be used outside authorised clinical trials.