Counterfeit weight loss injections have been a growing problem in the UK for years. Fake versions of Ozempic, Wegovy and Mounjaro have all turned up outside licensed pharmacies. Now retatrutide is the latest name in the trade.
Retatrutide has produced some of the biggest average weight loss results seen in obesity trials so far. Demand is high, even though it isn't approved anywhere in the world. A recent BBC investigation found counterfeit vials claiming to contain retatrutide being sold in gyms, beauty salons, hairdressers and on social media.1
This article explains what retatrutide is and how it differs from semaglutide and tirzepatide, the treatments already licensed for weight loss in the UK. We'll also look at why fake retatrutide may carry even more risk than counterfeit versions of approved GLP-1 medicines, and what to do if you've been affected.
What is retatrutide, and is it safe?
Retatrutide is an investigational, once-weekly injection developed by Eli Lilly. "Investigational" means it's still being tested in clinical trials.
It's designed to activate three hormone receptors in your body. Receptors are the docking points on your cells that hormones attach to. Two of them, GLP-1 and GIP, reduce appetite and help regulate blood sugar. You might know these two from Wegovy and Mounjaro.
The third is glucagon, which increases the amount of energy your body burns. Having all three in one molecule is what sets retatrutide apart from the GLP-1 medicines already available.
In a Phase 2 trial published in the New England Journal of Medicine, people on the highest dose lost an average of 24.2% of their body weight over 48 weeks. Those on placebo lost 2.1%.2
Topline results from the Phase 3 TRIUMPH-4 trial, announced by Eli Lilly in December 2025, went further. Average weight loss reached up to 28.7% over 68 weeks at the highest dose tested.3
So, is retatrutide safe? The honest answer is that we don't fully know yet.
The real drug is still unproven for everyday use. A fake version adds a second unknown on top of that.
Retatrutide is still in Phase 3 trials, and some studies aren't due to report final results until 2029. It hasn't been granted marketing authorisation (a licence to sell it) by the MHRA, the FDA or any other regulator.4
Not every drug that reaches Phase 3 goes on to be approved. Results can also look different in larger, more varied groups of people than in earlier, smaller studies. Long-term safety data takes years to build up. Until then, nobody, including Eli Lilly, can say retatrutide is safe for regular use outside of trials.
What's being sold illegally as "retatrutide" is much easier to judge. It is not safe. Nobody has verified what's in it, how strong it is, how well it was made, or whether it contains any retatrutide at all.
How does retatrutide differ from existing GLP-1 treatments?
Semaglutide (the active ingredient in Wegovy) works on one receptor: GLP-1. It slows digestion and reduces appetite.
Tirzepatide (the active ingredient in Mounjaro) goes a step further. It acts on both the GLP-1 and GIP receptors.
Retatrutide adds a third target: the glucagon receptor. Glucagon is usually linked to raising blood sugar. In this combination, though, its main role is thought to be metabolic, increasing how much fat your liver burns for energy.
At a glance: semaglutide targets one hormone receptor, tirzepatide two, and retatrutide three.
In trials so far, retatrutide has led to bigger average weight loss than seen in trials of medicines that target one or two receptors. Researchers think the third mechanism, on top of appetite suppression, may help explain that. But these are separate studies, so the results can't be compared directly.
That extra pathway is also why retatrutide needs more safety data before it reaches the market. Researchers need to understand how it behaves across a wide range of people, including those with existing heart, liver or thyroid conditions.
Is fake retatrutide more dangerous than fake Wegovy or Mounjaro?
Counterfeit weight loss injections aren't just a retatrutide problem. Fake Ozempic and Saxenda pens were being seized in the UK as early as 2023. Counterfeit Wegovy and Mounjaro have followed.7
So what's different about fake retatrutide? It's what the fake is imitating.
Wegovy and Mounjaro are licensed medicines. That means there's a genuine version to check a suspect product against. There's an approved dose, a patient information leaflet and a documented side effect profile. A counterfeit is still risky, but there's at least a clinical baseline to work from.
With a fake Wegovy or Mounjaro pen, there's at least a real product to compare it with. With fake retatrutide, there isn't.
Retatrutide doesn't have any of that yet. There's no approved dose, no patient information leaflet and no finished safety profile. The real drug is still years away from a possible licence.4
So when someone injects a product sold as retatrutide, they aren't just taking an unverified copy of a known medicine. They're taking an unverified copy of a medicine with no established safe use in the general public. If something goes wrong, there's no genuine version to compare it with. And there's no clear baseline for how your body should respond.
What are the safe, licensed alternatives?
If you're eligible, several weight loss treatments already have UK marketing authorisation and are dispensed by a registered pharmacy. They also come with proper clinical oversight, which no unlicensed product can offer.
For a full breakdown of which weight loss peptides are licensed in the UK and which are sold illegally, see our guide to peptides for weight loss.
Semaglutide
Available as Wegovy injectable pens or Wegovy oral tablets, semaglutide works on the GLP-1 receptor to reduce appetite and slow digestion. The most commonly reported side effects are digestive ones, like nausea and constipation. You're most likely to notice them while your dose is being increased.
Tirzepatide
Mounjaro targets both the GLP-1 and GIP receptors. It has shown strong average weight loss in clinical trials. Its side effects are broadly similar to semaglutide, and digestive symptoms are the most commonly reported.
Orlistat
Not suitable for, or don't want, an injectable or GLP-1 based treatment? Orlistat works differently. It reduces how much dietary fat your body absorbs. You take it as a capsule alongside meals.
Each of these is only prescribed after a proper clinical assessment. A pharmacist is also on hand throughout treatment to answer questions about dosing and side effects.
Look up any pharmacy on the GPhC register before you buy. It's free and only takes a minute.
Before you buy weight loss medicine from any online pharmacy, check that it's properly regulated. Every UK pharmacy dispensing prescription medicines must be registered with the General Pharmaceutical Council (GPhC). You can check registration for free on the GPhC's public register.
You can view Pharmica's GPhC registration here, and read independent patient reviews on Trustpilot. Checking these details for any pharmacy is the best way to confirm you're buying from a legitimate, regulated source.
Why and how are fake GLP-1 medicines like retatrutide being sold?
Demand for weight loss medication in the UK has grown fast. But you need a clinical assessment to get these treatments, and not everyone will pass. That might be down to existing conditions, safety precautions or BMI.
Some people who aren't eligible still want treatment. Criminal enterprises are taking advantage. They sell illicit, unregulated products, from semaglutide to retatrutide, with no clinical oversight.
Do not buy weight loss injections from gyms, salons, social media sellers or any website that isn't a registered pharmacy.
The MHRA's enforcement action shows how big this has become. In October 2025, its Criminal Enforcement Unit shut down the first illicit weight loss medicine production facility ever found in the UK. It was in a warehouse in Northampton.
The MHRA described the raid as the largest single seizure of trafficked weight loss medicines ever recorded by a law enforcement agency worldwide. Officers seized tens of thousands of empty pens and raw chemical ingredients. They also seized more than 2,000 unlicensed retatrutide and tirzepatide pens waiting to be sent to customers.5
In February 2026, a follow-up operation at two more sites, in Lincolnshire and Nottinghamshire, seized almost 2,000 more doses of unlicensed weight loss medicines. Again, these included retatrutide and tirzepatide.6
Eli Lilly has also reported more than 14,000 websites, adverts and social media posts that illegally market retatrutide. The company says it doesn't consider any retatrutide sold outside its own trials to be safe to use.1
What's actually in these counterfeit products?
Whether it's labelled semaglutide, tirzepatide or retatrutide, the problem is the same for anything bought outside a licensed pharmacy. You've got no way to independently confirm what's in the vial.
The MHRA has been direct about this. It warns that medicines from outside a registered pharmacy come with no guarantees about their contents. They may even be contaminated with toxic substances.5
The agency has also confirmed that some counterfeit weight loss injections seized in the UK contained insulin instead of the drug on the label. These were sold under other GLP-1 drug names.7 If you don't have diabetes, an unexpected dose of insulin can cause dangerously low blood sugar. Symptoms range from shaking and confusion to seizures and loss of consciousness.
Some fake injections have contained insulin. If you've used an unregulated product and feel shaky, sweaty or confused, get medical help straight away.
Many of these products also arrive as a powder that you have to mix yourself with sterile water. The calculations change from batch to batch. Get it wrong, even by a small margin, and every dose after that is the wrong strength.
There's also no guarantee the product was made in sterile conditions or stored properly in transit. Both affect whether an injectable is safe to use at all.
What are the potential side effects and risks?
In Eli Lilly's own trials, the most common side effects of genuine retatrutide have been digestive. They include nausea, diarrhoea, constipation and vomiting. They were mostly mild to moderate and happened more often while the dose was being stepped up. That's a similar pattern to other GLP-1 based medicines.2
This isn't just a retatrutide problem. The same risks apply to any counterfeit GLP-1 product.
With an unregulated product, the digestive effects can be a lot worse because the dose isn't reliable. Taking several times the intended amount, by accident or because the product is stronger than the label says, has been linked to severe, prolonged vomiting and diarrhoea.
There's also the added risk of contamination and infection at the injection site. You could have an allergic reaction to an unknown ingredient, or react to a completely different substance from the one advertised.
The side effects seen in trials were mainly digestive. With a counterfeit, unreliable dosing and contamination add risks that no trial has tested.
And there's no clinical oversight. A GP or prescriber would normally check for conditions that make a GLP-1 based medicine unsuitable, such as a personal or family history of certain thyroid cancers or pancreatitis. They'd also increase your dose gradually to keep side effects in check.
Buying an unregulated product removes every one of those safeguards, whatever GLP-1 medicine it's sold as.
Is it legal to buy or sell retatrutide in the UK?
The MHRA has stated plainly that retatrutide isn't approved for UK use. Outside authorised clinical trials, it says any product sold in the UK claiming to contain it is very likely to be illegal and potentially dangerous.5
Making, importing or supplying an unlicensed medicine without proper authorisation is an offence under the Human Medicines Regulations 2012.
The same principle applies to counterfeit versions of any licensed GLP-1 medicine. Selling or supplying weight loss injections from an unregistered source is illegal, whatever drug name is on the packaging. Buying them means taking a serious risk with your health.
Some products are labelled "research chemicals" or "not for human consumption" to try to get around this. That label doesn't change what happens once the product is injected into a person. It doesn't make the contents any safer or more predictable.
"Research chemical" and "not for human consumption" labels are red flags. They aren't a legal loophole.
When should you seek medical advice?
Speak to a GP, pharmacist or call NHS 111 if:
- You've taken a product claiming to be retatrutide, semaglutide, tirzepatide or any other weight loss injection and feel unwell, particularly with severe vomiting, dizziness, confusion, or symptoms of very low blood sugar such as shaking, sweating or sudden disorientation
- You're not sure what's in a product you've bought or been given
- You want to stop using an unregulated product and you're not sure how to do it safely
Think you've bought a fake or unlicensed medicine, or had a reaction to one? You can report it to the MHRA's Yellow Card Scheme online or by calling 0800 731 6789.8 Reports like these help the MHRA spot and act on new black market products.
Reporting a fake medicine helps the MHRA track down the people supplying it.
Frequently asked questions
Genuine retatrutide is still in Phase 3 clinical trials and hasn't been granted marketing authorisation by the MHRA, the FDA or any other regulator, so its full safety profile isn't established yet. Anything sold as retatrutide outside Eli Lilly's own trials hasn't been verified in any way, so it isn't safe to use.
Retatrutide is an investigational, once-weekly injectable weight-loss medicine developed by Eli Lilly. It works by activating three separate hormone receptors, GLP-1, GIP and glucagon, which is why it's sometimes called a "triple agonist". It has produced significant weight loss in clinical trials but isn't approved for use anywhere in the world.
How is retatrutide different from Wegovy and Mounjaro?
Wegovy (semaglutide) targets one receptor, GLP-1. Mounjaro (tirzepatide) targets two, GLP-1 and GIP. Retatrutide adds a third, the glucagon receptor, which researchers believe helps the body burn more fat for energy on top of reducing appetite.
Is it legal to buy retatrutide in the UK?
No. Retatrutide doesn't have UK marketing authorisation outside of clinical trials, and supplying an unlicensed medicine without proper authorisation is an offence under the Human Medicines Regulations 2012. The MHRA has said any product sold in the UK claiming to contain retatrutide is very likely to be illegal.
What are the side effects of retatrutide?
In Eli Lilly's own trials, the most commonly reported side effects of genuine retatrutide were gastrointestinal, including nausea, diarrhoea, constipation and vomiting, most often during dose increases. With an unregulated product, these effects can be considerably worse because the dose isn't reliable, and there's an added risk of contamination or an entirely different substance being present.
Is fake retatrutide more dangerous than fake Wegovy or Mounjaro?
In one important way, yes. Counterfeit Wegovy or Mounjaro at least imitate a licensed medicine with a known dose and a documented safety profile. Retatrutide doesn't have an approved dose or a finished safety profile at all, so there's no genuine version to compare a fake against if something goes wrong.
How can I tell if a weight loss injection is fake?
There's no reliable way to identify a counterfeit product by sight alone. The safest approach is to only get weight-loss medicines, including retatrutide, semaglutide or tirzepatide, from a registered pharmacy following a proper clinical assessment.
What should I do if I think I've bought a fake weight loss injection?
Stop using it and speak to a GP, pharmacist, or call NHS 111, especially if you feel unwell. You can also report it to the MHRA's Yellow Card Scheme online or by calling 0800 731 6789.
References
- BBC News. How the hunger for a new weight-loss drug is feeding an industry of fakes. BBC; 2026. bbc.co.uk
- Jastreboff AM, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. New England Journal of Medicine. 2023. doi:10.1056/NEJMoa2301972
- Eli Lilly and Company. Lilly's triple agonist, retatrutide, delivered weight loss of up to an average of 71.2 lbs...in first successful Phase 3 trial. Eli Lilly; 2025. investor.lilly.com
- ClinicalTrials.gov. The Effect of Retatrutide Once Weekly on Cardiovascular Outcomes and Kidney Outcomes in Adults Living With Obesity (TRIUMPH-Outcomes). NCT06383390. clinicaltrials.gov
- Medicines and Healthcare products Regulatory Agency. MHRA smashes major illicit weight loss medicine production facility in record seizure. GOV.UK; 2025. gov.uk
- Medicines and Healthcare products Regulatory Agency. MHRA disrupts second manufacturing facility suspected to be involved in the manufacture of illegal weight loss medicines. GOV.UK; 2026. gov.uk
- Medicines and Healthcare products Regulatory Agency. MHRA warns of unsafe fake weight loss pens. GOV.UK; 2023. gov.uk
- Medicines and Healthcare products Regulatory Agency. The Yellow Card scheme: guidance for healthcare professionals, patients and the public. GOV.UK; 2025. gov.uk
This article is intended for informational purposes only and does not replace professional medical advice. Always read the patient information leaflet supplied with your medication and speak to a healthcare professional if you have specific concerns.