Retatrutide: what early trials show and when it could reach the UK

​Retatrutide hasn't yet reached United Kingdom, but if you're looking for a GLP-1 medical weight loss program (like Mounjaro), Piko is the best option.​

Over the past year, retatrutide has been described in headlines as the “next generation” weight-loss injection – sometimes even nicknamed the “Godzilla” of jabs. Understandably, many people in the UK who are considering medical weight loss want to know what retatrutide actually is, what early retatrutide trials and retatrutide studies have found, and whether it might be an option for them in the future.

In this guide, we’ll walk through what we genuinely know so far, what’s still uncertain, and what this means for you if you’re exploring safe, regulated weight-loss treatments in the UK today.

What is retatrutide?

Retatrutide (also known as LY3437943) is an investigational obesity and metabolic drug being developed by Eli Lilly. It is not yet approved for routine clinical use anywhere in the world, including the UK.

It’s being studied as a potential treatment for:

• Obesity and overweight

• Type 2 diabetes

• Metabolic-related conditions (such as liver and kidney disease)

At the moment, retatrutide can only be accessed inside formal clinical trials. It cannot legally be prescribed on the NHS or by private clinics in the UK, and any website or provider claiming to sell “retatrutide pens” for home use is operating outside the law and outside safety regulations.

How does retatrutide work?

Retatrutide is often described as a “triple agonist” or “triple G” drug. That means it acts on three different hormone receptors at once:

• GLP-1 (glucagon-like peptide-1) – helps reduce appetite, slow stomach emptying and improve blood sugar.

• GIP (glucose-dependent insulinotropic polypeptide) – another “incretin” hormone that supports insulin release and may impact appetite and fat storage.

• Glucagon receptors – glucagon normally raises blood sugar and influences how the body uses fat and energy.

By stimulating all three pathways in a carefully balanced way, retatrutide appears to:

• Reduce hunger and food intake

• Improve blood sugar control in people with type 2 diabetes

• Increase energy expenditure and promote fat loss

This “triple signal” is why early studies suggest retatrutide may produce even greater weight loss than current GLP-1 agonists such as semaglutide (Wegovy) or the dual GLP-1/GIP agonist tirzepatide (Mounjaro).

What do retatrutide trials show so far?

The main phase 2 retatrutide trial in obesity

The most discussed retatrutide trial so far is a phase 2, double-blind, randomised trial in adults with obesity or overweight but without diabetes, published in The New England Journal of Medicine in 2023.

Key points from this retatrutide study:

• Participants: Adults with obesity or overweight (BMI ≥ 30, or ≥ 27 with complications)

• Duration: 48 weeks of treatment

• Dosing: Weekly injections of retatrutide at various doses vs placebo

• Results:

  • At the highest doses (8 mg and 12 mg), average weight loss reached around 22–24% of body weight at 48 weeks.

  • Many participants lost more than 20% of their starting weight.

  • Weight loss was still trending downwards at the end of the study, suggesting the full effect may not yet have been reached.

These levels of weight loss are in the same range – or slightly higher – than what’s been seen in the most potent GLP-1 and dual agonist drugs in development so far.

Retatrutide in people with type 2 diabetes

Another phase 2 retatrutide trial looked at adults with type 2 diabetes. In that study:

• Retatrutide led to:

  • Clinically meaningful reductions in HbA1c (long-term blood sugar marker)

  • Robust weight loss compared with placebo and with dulaglutide (a GLP-1 agonist)

• The safety profile was broadly similar to other GLP-1-based drugs, with mainly gastrointestinal side effects.

A separate analysis focusing on body composition showed that the proportion of lean mass lost with retatrutide was similar to other obesity treatments, despite the larger total weight-loss effect.

Liver and metabolic health

A substudy in people with obesity and metabolic dysfunction-associated steatotic liver disease (MASLD) found that retatrutide produced substantial reductions in liver fat, alongside its weight-loss effects.

Taken together, early clinical studies of retatrutide suggest:

• Very large average weight loss (often >20% of body weight at higher doses)

• Meaningful improvements in blood sugar control

• Potential benefits for liver and broader cardiometabolic health

However, these remain trial data – mostly from phase 2 – with relatively limited follow-up.

Key retatrutide studies: benefits and side effects

Benefits seen in retatrutide studies

Across early retatrutide trials, the main observed benefits have included:

• Substantial weight loss (15–24% or more in some cohorts)

• Improved blood sugar and HbA1c in type 2 diabetes

• Improved cardiometabolic markers, such as:

  • Blood pressure

  • Lipids

  • Liver fat (in MASLD substudies)

• Once-weekly injection, similar in convenience to other modern weight-loss injections

Side effects and tolerability

Like other incretin-based weight loss injections, retatrutide is associated mainly with gastrointestinal side effects, including:

• Nausea

• Vomiting

• Diarrhoea

• Constipation

• Abdominal discomfort

In trials, these side effects were usually:

• Dose-dependent (more common at higher doses)

• Most prominent during dose escalation, then often settled

• Managed using gradual titration schedules

Discontinuation rates in trials have been relatively low, but long-term safety data are still limited.

Importantly, because retatrutide also acts on glucagon receptors, regulators will pay close attention to potential effects on:

• Heart and cardiovascular risk

• Pancreas and gallbladder

• Liver and kidney function

These questions are exactly what ongoing phase 3 clinical trials are designed to answer.

Limitations of current retatrutide studies: what we still don’t know

While early retatrutide studies are promising, there are important limitations:

• Short-to-medium term only
  Most data so far cover around 1 year of treatment. We don’t yet know:

  • How sustainable weight loss is over multiple years

  • What happens when people stop the drug

• Trial populations, not real-world use
  Clinical trials typically involve:

  • Strict inclusion/exclusion criteria

  • Frequent monitoring and support
    Real-world patients may have more complex health problems, different adherence patterns and different risks.

• Long-term safety
  Longer, larger phase 3 trials and outcome studies are needed to fully understand:

  • Cardiovascular outcomes

  • Rare side effects

  • Long-term impact on organs such as the liver, kidneys and pancreas

• Interactions with other drugs and conditions
  We still need more data on:

  • Use in older adults

  • People with advanced kidney or liver disease

  • People on multiple interacting medications

For all these reasons, it’s too early to say exactly who retatrutide will be suitable for, what the final licensed doses will be, or how it will be positioned compared with existing weight-loss drugs.

Is retatrutide available in the UK yet?

In short: no.

• Retatrutide is not approved by the MHRA, FDA, EMA or any other major regulator.

• It cannot be prescribed legally on the NHS or through UK-regulated private clinics.

• Any retatrutide trial happening in or including the UK is strictly controlled, with participants enrolled through official clinical research channels.

Some UK-based websites have published patient-facing guides that clearly state retatrutide is not legal or licensed in the UK and highlight safer alternatives such as Wegovy and Mounjaro, which are approved under specific criteria.

So if you see a site or social-media seller offering to “ship retatrutide pens” or “start you on Triple G injections” today, they are not operating within UK law or medical regulation.

What could the approval path look like? (2026 and beyond)

Many commentators speculate that retatrutide might be approved around 2026, but this is not guaranteed.

What we can say at this stage:

• Retatrutide is now in phase 3 trials across several programmes, including:

  • Obesity and overweight

  • Type 2 diabetes (TRANSCEND-T2D)

  • Chronic kidney disease and cardio-renal outcomes (e.g. TRANSCEND-CKD, TRIUMPH-Outcomes)

• These studies will run for several years, with some primary completion dates not expected until the late 2020s.

If the results of the phase 3 retatrutide trials confirm strong benefits and an acceptable safety profile, the company may then apply for regulatory approval in:

• The US (FDA)

• The EU (EMA)

• The UK (MHRA), followed by NICE in England and equivalent bodies in Scotland, Wales and Northern Ireland

Realistically:

• Earliest potential approvals for some indications may be mid- to late-2026, but

• Delays or negative findings are always possible, and

• Availability on the NHS will depend on separate cost-effectiveness decisions.

So it’s better to think of retatrutide as a promising future option – not a guaranteed near-term solution.

Why you should be cautious about “retatrutide” products online

Because early retatrutide studies showed such striking weight-loss results, a parallel black market has already emerged:

• UK investigations have uncovered Telegram and social-media sellers promoting so-called “Triple G” or “retatrutide” jabs, often targeting young people and those frustrated with limited access to legal weight-loss drugs.

• The MHRA and police have raided facilities in England producing counterfeit weight-loss pens containing “retatrutide” or other ingredients, seizing thousands of unlicensed products.

• Health experts and patient-safety organisations have warned that none of these products are the genuine investigational drug, and they may contain:

  • Incorrect doses

  • Completely different medicines (including insulin)

  • Contaminants or unsafe excipients

Using these unregulated products carries serious risks:

• Infection from poor manufacturing or handling

• Unpredictable side effects

• Potential overdoses or dangerous under-doses

• No medical monitoring or follow-up

Bottom line:
If you are being sold “retatrutide pens” or “Triple G jabs” online, via Instagram, TikTok, Telegram, beauty salons or informal “clinics”, it is not legitimate retatrutide from a regulated supply chain, and you should avoid it.

Evidence-based weight-loss options available in the UK today

While you cannot access retatrutide legally in the UK yet, there are proven and regulated medical options available now. These include:

1. GLP-1 and dual-agonist weight-loss injections

Subject to eligibility and supply, certain weight-loss injections are licensed in the UK, for example:

• Semaglutide (Wegovy) – a GLP-1 agonist

• Tirzepatide (Mounjaro) – a dual GLP-1/GIP agonist

They are typically considered for:

• Adults with a high BMI (usually ≥30, or ≥27 with weight-related conditions)

• People who have already tried lifestyle measures without sufficient success

Each medicine has:

• Specific NHS criteria

• Private prescribing criteria

• Known side-effect profiles and monitoring requirements

2. Other prescription medications

Depending on your history and medical profile, a doctor might consider:

• Non-incretin oral weight-loss drugs

• Medications targeting appetite, absorption or metabolic pathways

• Treatment of related issues (e.g. insulin resistance, sleep apnoea, depression)

3. Structured lifestyle and behavioural programmes

Medications usually work best when combined with:

• Personalised nutrition and activity guidance

• Behavioural and psychological support

• Monitoring of sleep, stress and other lifestyle factors

That’s the logic behind digital weight-management programmes that combine doctor-led care, medication (when appropriate) and ongoing coaching or app-based support.

How Piko supports safe medical weight loss in the UK

Piko is a UK-regulated digital weight-loss clinic. While we cannot prescribe retatrutide (no-one legitimately can at this stage), we do support patients with safe, evidence-based options that are approved today.

Through Piko, adults in the UK can:

• Book an online appointment with a UK-registered doctor to discuss medical weight loss.

• Complete a detailed assessment of:

  • Weight history

  • Medical conditions and medications

  • Mental health and lifestyle factors

• If clinically appropriate, be offered:

  • Licensed weight-loss injections (such as GLP-1 or dual-agonist medications) when available and medically suitable

  • A personalised weight-loss programme, including lifestyle, nutrition and behavioural support

• Track progress over time through digital tools and regular check-ins.

We focus on:

• Safety first – only prescribing licensed medications from regulated pharmacies.

• Realistic expectations – explaining what current drugs can and can’t do.

• Sustainable change – combining medication with broader lifestyle support rather than quick-fix promises.

If you’re interested in exploring current medical options, you can:

• Take a short eligibility quiz for Piko’s weight-loss programme.

• Book an online consultation with a Piko doctor to discuss your situation in detail.

Frequently asked questions about retatrutide trials and studies

Is retatrutide available in the UK now?

No. Retatrutide is not approved by the MHRA, NICE or any other UK body and is only available inside controlled clinical trials. Any product marketed as retatrutide for home use in the UK is unlicensed and unregulated.

When might retatrutide be approved?

If ongoing phase 3 retatrutide trials are positive and regulatory submissions proceed smoothly, some commentators think approvals could happen from 2026 onwards. But this is not guaranteed and depends entirely on future trial results and regulatory decisions.

How much weight do people lose on retatrutide in trials?

In the main phase 2 obesity retatrutide study, people on the highest doses lost around 22–24% of their body weight on average after 48 weeks, with weight still trending downwards at the end of the trial.

Is retatrutide safer or riskier than Wegovy or Mounjaro?

We don’t know yet. Early trials suggest a similar pattern of side effects (mainly gastrointestinal) but with a stronger weight-loss effect. However, long-term safety data and large-scale outcome trials are still underway, and regulators will look very closely at cardiovascular, liver, kidney and other risks before approving it.

Can my doctor prescribe retatrutide “off-label”?

No. Because retatrutide is not licensed for any indication, it cannot be prescribed off-label in the UK. The only legitimate way to receive retatrutide is by being formally enrolled into an approved clinical trial.

What should I do if I’ve already bought “retatrutide” online?

If you have obtained a product marketed as “retatrutide” from an unregulated source:

• Stop using it and do not inject further doses.

• Speak to your GP or an urgent care service, especially if you’ve had side effects.

• Keep any packaging – it may be useful if regulators investigate the supplier.

• Consider reporting the seller to:

  • The MHRA Yellow Card scheme

  • Trading Standards or the platform where you found it

And for the future, only consider weight-loss medications prescribed by qualified clinicians and dispensed by licensed pharmacies.

What can I do now if I’m interested in medical weight loss?

You don’t have to wait for retatrutide to start making progress.

Right now, you can:

• Discuss licensed weight-loss medications with a clinician.

• Explore a structured digital programme like Piko, which combines:

  • Online doctor assessment

  • Medication (when appropriate)

  • Ongoing lifestyle and behavioural support

• Focus on sleep, stress, movement and nutrition – which still make a major difference, with or without medication.

If and when retatrutide is eventually approved, you’ll be in a much better position to consider it alongside other options, with guidance from your healthcare team.