Retatrutide UK: What Is It & When Will It Be Available?

What is retatrutide?

Retatrutide is a new medicine for weight loss. It is being developed by Lilly, the same company that manufactures weight loss jab Mounjaro (tirzepatide).

What makes retatrutide different from other weight-loss drugs is that it is a 'triple agonist,' meaning it targets three hormones (GLP-1, GIP, and glucagon) that reduce your appetite, increase calorie burning, and help control your blood sugar. This 'triple action' may make it the most effective weight loss drug to date.

Retatrutide has recently completed phase 3 of a clinical trial to assess its safety and effectiveness. It has not yet been approved for use in the general population.

What is a ‘retatrutide peptide’?

Retatrutide is classified as a synthetic peptide — a short chain of amino acids engineered in a lab to mimic the signals your body's own hormones send.

Unlike small-molecule drugs (like tablets), peptide-based medicines like retatrutide work by binding to specific hormone receptors and activating them, which is why they need to be given by injection rather than taken orally.

The retatrutide peptide is unique in that it has been designed to activate three separate receptors simultaneously, something no other approved weight loss drug currently does.

What does retatrutide do?

Retatrutide is a medicine that can make it easier to lose weight when combined with a healthy diet and regular exercise. It also helps control blood sugar levels in people with type 2 diabetes.

The medicine works by targeting the receptors for three hormones: Glucagon-like peptide-1 (GLP-1), Glucose-dependent insulinotropic polypeptide (GIP), and glucagon, and mimicking their effects. These three hormones work together to help stabilise blood sugar levels and make weight loss easier.

Glucagon-like peptide-1 (GLP-1)

This hormone is produced naturally in your intestine (gut). The synthetic version of this hormone is the active ingredient in weight loss drugs Wegovy (semaglutide) and Saxenda (liraglutide).

GLP-1 helps with blood sugar control and weight loss by:

• Stimulating your pancreas to release insulin, which helps control your blood sugar
• Slowing the rate at which food passes from your stomach to your intestine, which helps you feel full for longer
• Stopping your liver from releasing extra glucose into your blood, which helps to manage your blood sugars and reduces insulin resistance
• Sending signals to your brain that you are full and helping reduce cravings (food noise) by 'calming' your brain's reward centres

Glucose-dependent insulinotropic polypeptide (GIP)

This is another gut hormone that helps you lose weight and regulates your blood sugar. It is used in combination with GLP-1 in the weight-loss medications Zepbound (US) and Mounjaro (UK) - known as dual GIP/GLP-1 receptor agonists. GIP can also help reduce the nausea that can occur as a side effect of GLP-1 drugs.

It helps with weight loss and blood sugar management by:

• Increasing insulin production in your pancreas to keep your blood sugar levels in the normal range
• Suppressing your appetite, reducing cravings and keeping you feeling full for longer (when combined with GLP-1)
• Optimising the way your body stores fat and uses fat and glucose for energy

Glucagon

Glucagon is a peptide hormone produced by the pancreas that prevents blood sugar from getting too low. When combined with gut hormones like GLP-1 and GIP, it can help with weight loss by:

• Helping your body burn more calories by increasing your overall metabolic rate
• Stimulating your liver and fat cells to break down fats for energy rather than storing them
• Signalling to your brain that you are full, meaning you eat less food

Retatrutide is currently the only weight-loss medication to contain glucagon.

How do you take retatrutide?

Once approved, retatrutide will be available as a once-weekly injection. The exact dose is currently unknown, but it is expected to follow a dosing schedule similar to other weight loss injections, starting at a low dose and gradually increasing to a maximum maintenance dose.

What are the benefits of retatrutide?

As an investigational medication, the exact benefits of retatrutide are not yet fully known. Clinical trials suggest the new weight loss drug may offer significant benefits over other similar medications, including:

• Significantly more weight loss when compared to similar medications
• Improved blood sugar levels
• A large reduction in harmful fat, such as the fat around your abdominal organs (visceral fat) and liver fat, both of which can lead to serious health conditions, including Metabolically Active Steatotic Liver Disease (MASLD), type 2 diabetes, heart disease and stroke
• Improved heart health
• Improved pain in patients with knee osteoarthritis
• Potential improvement in conditions such as obstructive sleep apnoea, polycystic ovarian syndrome (PCOS), and some types of kidney disease

Is retatrutide safe?

Retatrutide has not yet been approved by any regulatory agency, including the FDA in the United States and the MHRA in the UK, and its safety is still being evaluated.

Unfortunately, counterfeit (fake) medications claiming to be retatrutide are currently circulating on the black market. These medications are untested and contain unknown ingredients that may be harmful to your health. The manufacturer of retatrutide, Lilly, has issued warnings to the public about the dangers of buying counterfeit medication.

Retatrutide side effects

As it has not yet been approved for use, information on the side effects ofretatrutide is limited. Once the medication becomes available, a full list of possible side effects will be included in the patient information leaflet.

Currently, the potential side effects of retatrutide appear to be similar to those of Wegovy and Mounjaro. Not everyone gets side effects, and most are mild and improve as your body adjusts to the medication. Your GP or pharmacist can advise you on managing side effects if you have them.

Common side effects of retatrutide include:

• Nausea (feeling sick)
• Vomiting (being sick)
• Diarrhoea
• Constipation

In clinical trials, some patients also reported the following side effects:

• Increased heart rate: This is mild and depends on the dose of retatrutide you receive. It usually resolves after a few months.
• Changes in skin sensation: Around 7% of participants reported changes in skin sensation, such as tingling or hypersensitivity.
• Redness, swelling, pain or itching at the injection site

How effective is retatrutide for weight loss?

Retatrutide has now completed the Phase 3 clinical trial to assess its effectiveness and safety.

This was known as the TRIUMPH-1 trial and evaluated 2,339 participants over 80 to 104 weeks. The participants were given increasing doses of retatrutide, starting at 4 mg, then 9 mg, and finally 12 mg.

The main results of the trial were as follows:

• Patients taking the maximum dose (12mg) lost an average of 70.3 lbs (28.3%) over 80 weeks
• Participants with a baseline body mass index (BMI) of 35 or above lost an average of 85 lbs (30.3%) over 104 weeks
• 45.3% of patients taking the maximum 12 mg dose lost 30% or more of their starting body weight — a result normally seen after weight loss (bariatric) surgery
• The study also found significant improvements in key markers for metabolic syndrome, such as waist circumference, blood pressure, and harmful blood fats such as triglycerides and non-HDL cholesterol

How does retatrutide compare to other weight loss medications?

Retatrutide targets three hormones to aid weight loss, unlike other weight loss medications that target one or two. The results of clinical trials indicate that this may make it more effective for weight loss when compared to otherapproved drugs like Wegovy (semaglutide), which targets one hormone, and Mounjaro (tirzepatide), which targets two.

Retatrutide vs Wegovy at a glance

Retatrutide vs Mounjaro at a glance

H2: When will retatrutide be available in the UK?

It isn't known exactly whenretatrutide will be available in the UK, but it is unlikely to be approved before 2027. Once approved, the drug is likely to be available on a private prescription first, with NHS availability expected later.

Because retatrutide is still legally unavailable in the UK, any products currently claiming to contain it are unregulated, counterfeit, or unsafe. If you suspect a medication is fake or being sold illegally, you can report it through the MHRA Yellow Card Scheme.

At Pharmacy Online, we expect to offer retatrutide as part of our comprehensive weight loss service when the medication has been approved.

How much will retatrutide cost?

Retatrutide has no official price yet — it hasn't been approved by the MHRA (UK) or FDA (US). But here's what we know:

• Expected UK price (post-approval) will likely be in line with Mounjaro, which runs £140–£370/month privately depending on dose. NHS availability would come later and at a subsidised cost.
• Expected US launch price is being estimated by analysts to be between $900–$1,500/month, with insurance coverage uncertain.
• FDA approval in 2026 is considered unlikely (prediction markets put it at ~27%). UK approval will likely follow that, so realistic availability is 2027 at the earliest — and with private prescription first.

This article was written by Claudia Jackson RN Freelance Health Content Writer.

This article was medically reviewed by Umar Razzaq - Clinical Pharmacist at Pharmacy Online (GPhC: 2064448).

Sources and further reading

Retatrutide—A Game Changer in Obesity Pharmacotherapy PubMed

A Study of Retatrutide (LY3437943) in Participants Who Have Obesity or Overweight (TRIUMPH-1) NIH

What to know about retatrutide: An investigational triple hormone receptor agonist Lilly

Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial The New England Journal of Medicine