Retatrutide (Reta) is not approved by the MHRA and cannot legally be prescribed or purchased in the UK as of August 2026.
It is a triple agonist (GIP, GLP-1, glucagon) showing up to 24% body weight loss in Phase 2 trials. Phase 3 trials are ongoing. Last updated: by Rachel Orriss, Level 3 Nutrition Coach.
What should you eat on Retatrutide (or any triple agonist)?
The key nutrition priority on any triple agonist is high protein intake, 1.2 to 1.6g per kg of body weight per day to prevent muscle loss. Because appetite is severely suppressed, meal replacement shakes such asFormula 1 combined with Protein Drink Mix are the most practical way to hit protein targets when eating full meals feels impossible. Prioritise protein at every meal, include resistance exercise 2–3 times per week, and ensure adequate micronutrient intake through a quality multivitamin.
Is Retatrutide safe?
Retatrutide is still in Phase 3 clinical trials and its full safety profile is not yet established. Phase 2 data showed it was generally well tolerated, with the most common side effects being nausea, vomiting, and diarrhoea, similar to other GLP-1 medications. Because it is not approved by the MHRA, it cannot be legally prescribed or obtained in the UK. Any source offering Retatrutide in the UK is operating illegally and the product's safety, purity, and dosing cannot be verified.
What are the side effects of Retatrutide?
Based on Phase 2 trial data, the most commonly reported side effects of Retatrutide include nausea, vomiting, diarrhoea, decreased appetite, and injection-site reactions. The full side-effect profile will not be known until Phase 3 trials are complete. The glucagon component may also increase the risk of lean muscle mass loss compared to existing GLP-1 medications, making high protein intake especially important.
How does Retatrutide work?
Retatrutide simultaneously activates three hormone receptors: GIP (glucose-dependent insulinotropic polypeptide), GLP-1 (glucagon-like peptide-1), and glucagon. The GLP-1 and GIP pathways suppress appetite and improve insulin sensitivity. The glucagon pathway increases energy expenditure, the rate at which the body burns calories at rest. This triple mechanism is why Phase 2 trials showed greater weight loss (up to 24% of body weight) than existing dual agonists like Mounjaro (tirzepatide).
Eating Well on Retatrutide (Reta) UK, Why Nutrition Still Matters When You're Not Hungry
Retatrutide, nicknamed "Reta", is the most talked-about next-generation weight-loss drug in the world right now. As a triple agonist targeting GIP, GLP-1, and glucagon receptors simultaneously, early trial data suggests it could produce greater weight loss than Mounjaro or Wegovy. But Retatrutide is not approved by the MHRA and cannot legally be prescribed or purchased in the UK. This guide explains what the science tells us about nutrition on triple agonists, why muscle loss is a serious risk, and what you can do right now to protect your results.
Quick answer: Retatrutide is not yet approved in the UK, it cannot be legally prescribed or obtained here. If you are interested in structured weight loss support right now, a high-protein routine built around Formula 1 and Protein Drink Mix delivers the same satiety and muscle-preservation benefits that nutrition researchers recommend alongside any GLP-1 or triple agonist therapy. Also see: eating well on Mounjaro · eating well on Wegovy · what to eat after stopping injections.
This guide is for you if...
- You are on Mounjaro or Wegovy and want to optimise your nutrition now
- You are following the Retatrutide trials and want to understand the science
- You want to protect your muscle and metabolism on any weight-loss injection
- You are preparing your nutrition habits ahead of any future approval
This guide is NOT for you if...
- You are looking to obtain Retatrutide. It is not legal in the UK
- You want a specific Reta diet plan. The drug is not approved and no clinical protocols exist yet
- You are seeking medical advice, always consult your prescribing doctor
What is Retatrutide (Reta)? Retatrutide is an investigational triple agonist drug developed by Eli Lilly that simultaneously activates three hormone receptors: GIP (glucose-dependent insulinotropic polypeptide), GLP-1 (glucagon-like peptide-1), and glucagon. This triple mechanism is designed to suppress appetite more powerfully than existing dual agonists like tirzepatide (Mounjaro), increase energy expenditure via the glucagon pathway, and improve metabolic function. Phase 3 clinical trials are ongoing. As of August 2026, it has not received regulatory approval in the UK, the EU, or the USA.
Why is everyone talking about Retatrutide?
Phase 2 trial data published in 2023 showed that participants taking the highest dose of Retatrutide lost an average of 24% of their body weight over 48 weeks, significantly more than the 15–20% seen with semaglutide (Wegovy) and comparable to the best results seen with tirzepatide (Mounjaro). The glucagon component is what makes Reta different: it does not just suppress appetite, it also appears to increase the rate at which the body burns energy, even at rest.
For context, Mounjaro targets two receptors (GIP and GLP-1). Retatrutide targets three. That additional glucagon pathway is why researchers and patients are watching it so closely, and why the nutrition considerations are even more important than with existing injections.
Phase 2 data is promising but not definitive. Phase 3 trials are currently ongoing and results are expected in 2025–2026. Until Phase 3 data is published and regulatory submissions are made, Retatrutide remains an investigational compound only.
Retatrutide vs Mounjaro vs Wegovy vs Ozempic. How do they compare?
This table covers the key differences between the four most-discussed weight-loss injections. Note that Retatrutide data comes from Phase 2 trials only and is not yet approved anywhere in the world.
| Ozempic / Wegovy (semaglutide) | Mounjaro (tirzepatide) | Retatrutide (Reta) | |
|---|---|---|---|
| Drug type | GLP-1 agonist | GIP + GLP-1 dual agonist | GIP + GLP-1 + glucagon triple agonist |
| Developer | Novo Nordisk | Eli Lilly | Eli Lilly |
| Average weight loss | ~15% body weight (72 weeks) | ~20% body weight (72 weeks) | ~24% body weight (48 weeks, Phase 2) |
| Muscle loss risk | Moderate (25–40% of weight lost) | Moderate (25–40% of weight lost) | Potentially higher due to glucagon pathway |
| UK approval status | Approved (MHRA) | Approved (MHRA) | Not approved, Phase 3 trials ongoing |
| Can I get it in the UK? | Yes, via NHS or private prescription | Yes, via private prescription | No, illegal to sell or prescribe in the UK |
| Protein priority | 1.2–1.6g per kg/day | 1.2–1.6g per kg/day | 1.2–1.6g per kg/day (likely higher need) |
The muscle-loss problem, and why it is worse with triple agonists
Every GLP-1 medication carries a muscle-loss risk. When appetite is suppressed and calorie intake drops sharply, the body does not automatically burn fat, it breaks down muscle tissue for energy too. This is called lean mass loss, and it is one of the most underreported side effects of weight-loss injections.
What the Mounjaro and Wegovy data shows
Studies on semaglutide and tirzepatide consistently show that 25–40% of total weight lost comes from lean mass (muscle), not fat. For a person losing 20kg on Wegovy, that could mean 5–8kg of muscle lost, which slows metabolism, reduces strength, and makes weight regain far more likely when the medication stops.
Why Retatrutide may amplify this risk
The glucagon component of Retatrutide increases energy expenditure, but glucagon also promotes the breakdown of stored energy, including muscle glycogen and protein. Early trial data does not yet provide detailed lean mass composition data, but nutrition researchers have flagged that the greater appetite suppression and higher energy expenditure seen with triple agonists could accelerate lean mass loss if protein intake is not actively managed.
The rebound risk is real. The same pattern seen with Wegovy and Mounjaro will almost certainly apply to Retatrutide: when the medication stops, appetite returns rapidly. If muscle mass has been lost during the treatment period, the body's resting metabolic rate is lower, meaning weight regain happens faster and is harder to reverse. Building and protecting muscle during any weight-loss injection programme is not optional. It is essential.
Start protecting your muscle today with Formula 1 + Protein Drink Mix
Same-day dispatch before 2pm · Genuine Herbalife · Fast UK deliveryWhat nutrition researchers recommend on triple agonists
While there are no published clinical nutrition protocols specifically for Retatrutide (the drug is not yet approved), the principles established for GLP-1 and dual agonist therapy apply, and likely apply with even greater urgency given the glucagon component.
The three non-negotiables
- High protein intake1.2 to 1.6g per kg of body weight per day, every day
- Resistance exercise2 to 3 sessions per week to signal muscle retention
- Micronutrient sufficiency a quality multivitamin to cover deficiencies caused by reduced food intake
These are not optional extras. They are the difference between losing fat and losing muscle. On a drug as powerful as Retatrutide, where appetite suppression may be more severe than anything currently available, the risk of under-eating protein is significant.
How much protein do you actually need?
Use the table below to find your daily protein target based on body weight.
| Body weight | Minimum (1.2g/kg) | Target (1.6g/kg) | How to hit it with Herbalife |
|---|---|---|---|
| 60kg | 72g | 96g | 2 shakes (72g) + 1 protein-rich meal |
| 70kg | 84g | 112g | 2 shakes (72g) + 1–2 meals with protein (40g) |
| 80kg | 96g | 128g | 2 shakes (72g) + 2 meals with protein (30g each) |
| 90kg | 108g | 144g | 2 shakes (72g) + 2 meals with protein (40g each) = 152g |
| 100kg | 120g | 160g | 2 shakes (72g) + 2 protein-rich meals (50g total) + 1 bar (10g) = 132g |
Formula 1 with Protein Drink Mix provides approximately 36g of protein per serving. Two shakes per day = 72g protein, a strong foundation for any injection user.
Micronutrient deficiency risk
When food intake drops significantly, as it does on any GLP-1 or triple agonist, micronutrient intake drops with it. Deficiencies in key vitamins and minerals can cause fatigue, hair loss, poor immune function, and impaired muscle recovery.
Vitamin D
Critical for muscle function and immune health. Deficiency is already widespread in the UK.
B12
Essential for energy metabolism and nerve function. Low intake on a suppressed appetite increases deficiency risk.
Iron
Particularly important for women. Fatigue on injections is often attributed to the drug when iron deficiency is the real cause.
Magnesium
Low magnesium impairs sleep, muscle recovery, and insulin sensitivity.
Zinc
Reduced food variety on injections commonly leads to inadequate zinc intake.
Calcium
Bone density matters especially when losing weight rapidly.
Formula 1 provides 23 essential vitamins and minerals per serving, making it one of the most practical ways to maintain micronutrient sufficiency when appetite is severely suppressed.
What to do right now, 3-step plan
Start with two Formula 1 shakes made with Protein Drink Mix, that gives you 72g before you eat a single meal.
Bodyweight exercises at home, squats, press-ups, resistance bands, are enough to signal muscle retention.
Formula 1 covers 23 vitamins and minerals per serving. If you are only eating one or two small meals per day, a quality multivitamin alongside your shakes is essential.
How Herbalife supports nutrition on weight-loss injections
Genuine Herbalife products · Fast UK delivery · No minimum order
Formula 1 Nutritional Shake Mix
21g protein per serving with Protein Drink Mix. 23 vitamins and minerals. The foundation of any injection-user nutrition plan.
Shop Formula 1Protein Drink Mix
Add to Formula 1 to boost protein to 36g per shake. Essential for hitting 1.2–1.6g/kg targets when appetite is suppressed.
Shop Protein Drink MixFull Weight Loss Range
Bars, shakes, teas, and supplements. Everything you need to support your nutrition on any weight-loss injection programme.
Shop AllSample high-protein day on a weight-loss injection
This is a realistic example for someone weighing 80kg targeting 120–128g of protein per day.
36g protein · 23 vitamins and minerals · Takes 2 minutes to make
15–20g protein · Easy to eat even with low appetite
25–35g protein · Keep portions small if appetite is low, protein first
36g protein · Second shake keeps totals on track without forcing a large meal
25–35g protein · Even a small portion counts, do not skip protein at dinner
Total: approximately 137–162g protein. Adjust shake quantities and meal sizes to your own weight and tolerance.
Frequently asked questions
Can I buy Retatrutide in the UK?
No. Retatrutide has not been approved by the MHRA and cannot legally be prescribed or purchased in the UK. Any website offering to sell it is operating illegally.
When will Retatrutide be available in the UK?
Phase 3 trials are ongoing. If results are positive and Eli Lilly submits a regulatory application to the MHRA, approval could potentially follow in 2026 or 2027, but this is speculative. There is no confirmed UK launch date.
Is Retatrutide better than Mounjaro?
Phase 2 data suggests greater average weight loss with Retatrutide (up to 24%) compared to Mounjaro (15–22%). However, Phase 2 trials are smaller and shorter than Phase 3. Direct head-to-head comparison data does not yet exist. Mounjaro is approved, available, and has a well-established safety profile. Retatrutide does not.
What should I eat on Retatrutide?
Prioritise protein (1.2–1.6g per kg of body weight per day), include resistance exercise, and ensure adequate micronutrient intake. Formula 1 with Protein Drink Mix is the most practical way to hit protein targets when appetite is severely suppressed.
Will I lose muscle on Retatrutide?
There is a real risk of lean mass loss on any GLP-1 or triple agonist medication. The glucagon component of Retatrutide may increase this risk. High protein intake and resistance exercise are the two most evidence-based strategies for minimising muscle loss.
Can I use Herbalife on Mounjaro or Wegovy while waiting for Retatrutide?
Yes. Formula 1 and Protein Drink Mix are used by many of our customers who are currently on Mounjaro or Wegovy. The nutrition principles are identical, high protein, adequate micronutrients, resistance exercise.
Ready to protect your results on any weight-loss injection?
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