Weight loss drugs have dominated health headlines over the past few years. First came semaglutide (Ozempic, Wegovy), then tirzepatide (Mounjaro). Now there’s a new name generating serious attention in medical circles: retatrutide.

With Phase 3 trial results showing average body weight losses of nearly 30% — surpassing anything seen with Ozempic or Mounjaro — retatrutide is being described by some researchers as the most powerful weight loss drug ever tested. Here’s what we know so far, when it might be available in the UK, and what supplements matter if you’re on a weight loss journey right now.

What Is Retatrutide?

Retatrutide is an experimental weight loss drug developed by Eli Lilly, the same company behind Mounjaro (tirzepatide). It’s what’s known as a triple agonist — meaning it activates three separate hormone receptors simultaneously:

• GLP-1 (glucagon-like peptide-1) — the same receptor targeted by Ozempic and Wegovy, which reduces appetite and slows gastric emptying
• GIP (glucose-dependent insulinotropic polypeptide) — also targeted by Mounjaro, which improves insulin sensitivity and enhances the GLP-1 effect
• Glucagon receptor — the new addition, which increases energy expenditure and fat burning beyond what dual agonists achieve

By hitting all three receptors, retatrutide produces a more powerful effect on appetite suppression, metabolism and fat burning than either semaglutide or tirzepatide — which is reflected in the trial data.

What Do the Clinical Trial Results Show?

In December 2025, Eli Lilly released results from the TRIUMPH-4 Phase 3 trial — one of the largest in the retatrutide programme. The headline findings were striking:

• Participants taking the 12mg dose lost an average of 28.7% of their body weight at 68 weeks — equivalent to roughly 32kg on average
• Those on the 9mg dose lost an average of 26.4%
• Significant reductions in knee pain were also observed, with some participants becoming completely free of pain
• Additional benefits included improvements in cholesterol, triglycerides and blood pressure

To put that in context: Wegovy (semaglutide) produces around 15–17% weight loss in trials, and Mounjaro (tirzepatide) around 20–22%. Retatrutide’s 28.7% is in a different category entirely.

How Does It Compare to Ozempic and Mounjaro?

Side Effects and Safety

Like all GLP-1 class drugs, retatrutide carries a similar side effect profile — nausea, vomiting, diarrhoea and constipation are the most commonly reported, particularly at the start of treatment and when doses are increased.

The TRIUMPH-4 trial also identified a new side effect not commonly seen with semaglutide or tirzepatide: dysesthesia — an abnormal tingling or burning sensation in the skin. This occurred in 8.8% of participants on the 9mg dose and 20.9% on the 12mg dose, compared to less than 1% on placebo.

Discontinuation rates due to adverse events were also higher than with previous GLP-1 drugs — 12.2% on 9mg and 18.2% on 12mg. This is something regulators will scrutinise closely before approving the drug.

When Will Retatrutide Be Available in the UK?

As of mid-2026, retatrutide is not available in the UK on prescription or privately. The remaining core Phase 3 trials — TRIUMPH-1 and TRIUMPH-2 — are expected to report results by late 2026. Eli Lilly is expected to file for FDA approval (in the US) in late 2026 at the earliest.

UK approval via the MHRA typically follows US FDA approval by 12–18 months. The realistic timeline for UK NHS availability is 2028 or later, with private prescription access potentially arriving a little earlier.

Anyone offering retatrutide for sale in the UK right now is operating outside the law. It is not a licensed medicine in this country and should not be purchased from unregulated sources.

What Supplements Matter If You’re Focused on Weight Loss?

Whether you’re using a weight loss medication, following a calorie-controlled diet, or both — the right supplements make a significant difference to your results and your health. Here’s what matters most:

Protein Powder — The Most Important Supplement on a Weight Loss Journey

One of the biggest challenges with any significant weight loss — drug-assisted or not — is muscle loss. When you’re in a calorie deficit, your body breaks down both fat and muscle tissue. GLP-1 drugs dramatically reduce appetite, which often means people aren’t eating enough protein to preserve muscle mass.

Research suggests consuming 1.8–2.4g of protein per kg of bodyweight per day during a weight loss phase to minimise muscle breakdown. For many people on appetite-suppressing medications, hitting this target through food alone is very difficult — which is where protein powder becomes essential.

Good options: Dymatize ISO100 (very lean, high protein, easy on digestion), Optimum Nutrition Gold Standard Whey, or PHD Diet Whey for those wanting added fat-loss ingredients.

Creatine — Preserve Strength While You Lose Fat

Creatine is one of the most effective tools for maintaining strength and muscle mass during a calorie deficit. By supporting ATP production in muscle cells, it helps you maintain performance in the gym even when eating less — which in turn helps preserve the muscle you’ve worked to build.

3–5g of creatine monohydrate daily is the established effective dose. It’s cheap, unflavoured and well-tolerated.

Vitamins & Minerals — Cover Nutritional Gaps

When appetite is significantly suppressed — as it is on GLP-1 medications — it’s easy to fall short on key micronutrients. Vitamin D, B12, iron, zinc and omega-3 fatty acids are among the most commonly deficient in people eating very low calorie diets.

A quality multivitamin, omega-3 fish oil and vitamin D supplement are sensible daily additions for anyone significantly reducing their food intake. Browse our vitamins range for options across all price points.

Where to Buy Supplements in London

Buffalo Nutrition is at 132 Cricklewood Broadway, London NW2 3EE — North West London’s top-rated supplement store. We stock protein powders, creatine, vitamins and a wide range of health and performance supplements from 50+ brands.

• Open Monday to Saturday, 10:30am – 7pm
• Rated 4.9★ on Google with 184+ reviews
• Free UK delivery on orders over £50

Note: Buffalo Nutrition sells sports nutrition and health supplements only. We do not sell retatrutide, semaglutide, tirzepatide or any prescription weight loss medications.