Counterfeit weight loss injections have been a growing problem in the UK for years, with fake versions of Ozempic, Wegovy and Mounjaro all found circulating outside licensed pharmacies. Retatrutide is the latest name to be swept up in that trade. It has produced the largest average weight loss of any drug tested in an obesity trial to date, and demand for it is high, even though it hasn't been approved for use 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. It also looks at why fake retatrutide may carry even greater risk than counterfeit versions of already-approved GLP-1 medicines, and what to do if you're affected.
What is retatrutide, and is it safe?
Retatrutide is an investigational, once-weekly injectable medicine developed by Eli Lilly. It's designed to activate three separate hormone receptors in the body. Two of these, GLP-1 and GIP, reduce appetite and help regulate blood sugar. You'll likely already be familiar with these two from Wegovy and Mounjaro. The third, glucagon, increases the amount of energy the body burns. The combination of all three in a single 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, participants taking the highest dose of retatrutide 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, reported weight loss of up to 28.7% over 68 weeks at the highest doses tested.3
So, is retatrutide safe? The honest answer is we do not fully know yet. Retatrutide remains in Phase 3 trials, with some studies not due to report final results until 2029. It has not been granted marketing authorisation by the MHRA, the FDA, or any other regulator.4 Not every drug that reaches Phase 3 trials goes on to be approved, and results can look different in larger, more diverse populations than they did in earlier, smaller studies. Long-term safety data takes years to accumulate, and until that process is complete, nobody, including Eli Lilly themselves, can say that retatrutide is safe for regular use outside of trials.
What's currently being sold illegally as "retatrutide" is much simpler to define. It is not safe, because its content, strength, quality, or even whether what's being sold contains any retatrutide at all, has not been verified.
How does retatrutide differ from existing GLP-1 treatments?
Semaglutide (the active ingredient in Wegovy) works on a single receptor, GLP-1, to slow digestion and reduce appetite. Tirzepatide (the active ingredient in Mounjaro) goes a step further, acting on both the GLP-1 and GIP receptors.
Retatrutide adds a third target: the glucagon receptor. Glucagon is usually associated with raising blood sugar, but in this combination, its main effect is thought to be metabolic, increasing how much fat the liver burns for energy. Researchers believe this third mechanism, on top of appetite suppression, is responsible for retatrutide's greater weight loss results in trials compared with GLP-1 medicines that target one or two receptors.
That third mechanism is also why retatrutide needs more safety data and scrutiny before it reaches the market. Activating an additional hormone pathway means researchers have to establish how it behaves, and the effects it could produce, 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 a retatrutide-only problem. Fake Ozempic and Saxenda pens were being seized in the UK as early as 2023, and counterfeit Wegovy and Mounjaro have followed since.7 What's different about fake retatrutide is what it's actually imitating.
Wegovy and Mounjaro are both licensed medicines. That means there's a genuine version to compare a suspect product against - an approved dose, a patient information leaflet and a documented side effect profile. That by no means reduces the risk of a counterfeit medication, but it does mean that there is a legitimate and authorised equivalent that can be used as a clinical baseline.
Retatrutide doesn't have any of that yet, genuine or otherwise. There is no approved dose, no patient information leaflet, and no finished safety profile, because the real drug is still years away from potentially being licensed.4 So when someone injects a product sold as retatrutide, they're not just taking an unverified copy of a known medicine. They're taking an unverified copy of a medicine that doesn't have an established safe use in the general public at all. If something goes wrong, there's no genuine version to compare it against, and no clear baseline for how the body should be expected to 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, something no unlicensed product can offer.
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 gastrointestinal, such as nausea and constipation, particularly while the dose is being increased.
Tirzepatide
Mounjaro targets both the GLP-1 and GIP receptors and has shown strong average weight loss results in clinical trials. Its side effect profile is broadly similar to semaglutide, with gastrointestinal symptoms being the most frequently reported.
Orlistat
For people who aren't suitable for, or don't want, an injectable or GLP-1 based treatment, orlistat works differently, by reducing how much dietary fat the body absorbs. It's taken as a capsule alongside meals.
Each of these is prescribed only after a proper clinical assessment, with a pharmacist available to answer questions about dosing and side effects throughout treatment.
Before buying weight loss medicines from any online pharmacy, you should check that it's properly regulated. Every UK pharmacy dispensing prescription medicines must be registered with the General Pharmaceutical Council (GPhC) and registration can be checked for free on the GPhC's public register. Pharmica's own GPhC registration can be viewed here, and independent patient reviews can be found 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 medications in the UK has grown rapidly. But eligibility for these treatments also depends on a clinical assessment that not everyone will pass. Whether that's due to pre-existing conditions, safety precautions or BMI, there are people who are not eligible, but still want treatment. This is being exploited by criminal enterprises, who are selling illicit and unregulated products, from semaglutide to retatrutide, without any clinical oversight.
The scale of this has become clear as a result of the MHRA's enforcement action. In October 2025, the agency's Criminal Enforcement Unit dismantled the first illicit weight loss medicine production facility ever found in the UK, in a warehouse in Northampton. It 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, raw chemical ingredients, and more than 2,000 unlicensed retatrutide and tirzepatide pens awaiting dispatch to customers.5 In February 2026, a follow-up operation across two further sites in Lincolnshire and Nottinghamshire seized almost 2,000 more doses of unlicensed weight loss medicines, again including retatrutide and tirzepatide.6
Eli Lilly has also said it has reported more than 14,000 websites, adverts and social media posts illegally marketing retatrutide. The company says it does not consider any retatrutide sold outside its own trials to be safe to use.1
What's actually in these counterfeit products?
This is the problem with any product bought outside a licensed pharmacy, whether it's labelled as semaglutide, tirzepatide or retatrutide: there's no way to independently confirm what's in the vial. The MHRA has been direct about this, warning that medicines sourced outside a registered pharmacy carry no guarantees about their contents and may even be contaminated with toxic substances.5 The agency has also confirmed that some counterfeit weight loss injections seized in the UK, sold under other GLP-1 drug names, have contained insulin instead of the drug on the label.7 For someone who doesn't have diabetes, an unexpected dose of insulin can cause dangerously low blood sugar, with symptoms ranging from shaking and confusion to seizures and loss of consciousness.
Many of these products also arrive as a powder that the buyer has to reconstitute themselves with sterile water, using calculations that vary depending on the batch. Getting this wrong, even by a small margin, changes the strength of every dose that follows. There's also no guarantee of sterile manufacturing or proper storage during transport, both of which affect whether an injectable product is safe to use at all.
What are the potential side effects and risks?
In Eli Lilly's own trials, the most commonly reported side effects of genuine retatrutide have been gastrointestinal, including nausea, diarrhoea, constipation and vomiting. These were mostly mild to moderate and occurred more often during dose escalation, a pattern similar to that seen with 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, gastrointestinal effects can be considerably worse simply because the dose isn't reliable. Taking several times the intended amount, whether by accident or because the product is more concentrated than labelled, has been linked to severe, prolonged vomiting and diarrhoea. Beyond that, there's the added risk of contamination, infection at the injection site, an allergic reaction to an unknown ingredient, or a reaction to an entirely different substance than the one advertised.
There's also no clinical oversight built into any of this. 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 would also titrate the dose gradually to manage side effects. Buying an unregulated product removes every one of those safeguards, regardless of which 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 has not been approved for UK use. Outside of 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 Manufacturing, 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. Buying weight loss injections from an unregistered source is illegal regardless of which drug name is printed on the packaging, and products are sometimes marketed as "research chemicals" or "not for human consumption" to try to sidestep this. That labelling doesn't change what happens once the product is injected into a person, and it doesn't make the contents any safer or more predictable.
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 a product you've bought or been given actually contains
- You want to stop using an unregulated product and aren't sure how to do so safely
If you believe 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 are part of how the MHRA identifies and acts on new black market products.
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.