What is Retatrutide?
Retatrutide is a next-generation weight loss injection developed by Eli Lilly (same manufacturer as Mounjaro), designed to target three separate hormone receptors in the body: the GLP-1 receptor, the GIP receptor, and the glucagon receptor. This triple-agonist mechanism of action distinguishes it from currently available treatments such as Wegovy (which targets one receptor) and Mounjaro (which targets two).
By engaging all three receptors simultaneously, retatrutide aims to suppress appetite, regulate blood sugar levels and increase the body's metabolic rate and help increase energy expenditure and influence fat metabolism, though the exact contribution of each pathway is still being studied. In Phase 2 clinical trials, participants achieved an average weight reduction of up to 24.2% of their body weight over 48 weeks - a result that is higher than the weight loss rate achieved with other injectable weight loss treatments in comparable studies.
The treatment is currently in Phase 3 clinical trials and is not yet approved or available for purchase in the UK.
Retatrutide UK Availability - Where Can You Buy It?
Retatrutide is not currently available to buy in the UK. The treatment is still undergoing Phase 3 clinical trials conducted by Eli Lilly, and it has not yet been submitted for regulatory approval to the Medicines and Healthcare products Regulatory Agency (MHRA).
When will Retatrutide be available in the UK?
Based on the current clinical trial timeline, retatrutide Phase 3 trial results are expected to be published in late 2026 or 2027. Following this, Eli Lilly would need to submit a marketing authorisation application to the MHRA, which typically takes 12-18 months to review. This means retatrutide could realistically become available in the UK from 2028 at the earliest, though this timeline may change depending on trial outcomes and regulatory decisions.
How much will Retatrutide cost?
The price of Retatrutide in the UK has not yet been confirmed, as it has not received regulatory approval. However, based on the pricing of similar injectable weight loss treatments currently available in the UK, the expected cost may fall in a comparable range:
- Mounjaro (tirzepatide, dual agonist): from £159.99 per pen at Pharmica
- Wegovy (semaglutide, single agonist): from £119.99 per pen at Pharmica
Can you buy Retatrutide Peptide in the UK?
While retatrutide research peptides are being sold through unregulated online suppliers, it is strongly advised against purchasing retatrutide from these sources. There are significant safety concerns associated with buying weight loss treatments outside of regulated pharmacies.
If you are looking for a clinically proven, regulated weight loss treatment available now, Pharmica offers Mounjaro and Wegovy, both of which are MHRA-approved and dispensed by our registered pharmacists following an online consultation.
How does Retatrutide work?
Retatrutide works by mimicking and activating three naturally occurring hormones in the body that play key roles in appetite regulation, blood sugar management and metabolism:
- GLP-1 (glucagon-like peptide-1) - Promotes feelings of fullness after eating, slows gastric emptying (the rate at which food leaves the stomach), and stimulates insulin secretion to help regulate blood sugar levels. This is the same receptor targeted by Wegovy (semaglutide) and Mounjaro (tirzepatide).
- GIP (glucose-dependent insulinotropic polypeptide) - Enhances insulin secretion in response to food intake and helps prevent blood sugar spikes that can trigger hunger and cravings. This receptor is also targeted by Mounjaro (tirzepatide), alongside GLP-1.
- Glucagon receptor - Stimulates the breakdown of stored fat for energy and increases the body's resting metabolic rate. This is the unique third receptor that retatrutide targets, which is not activated by either Wegovy or Mounjaro.
The combined activation of all three receptors creates a synergistic effect: appetite is suppressed through GLP-1 and GIP activity, while the glucagon receptor increases fat burning and energy expenditure. This dual approach - reducing calorie intake while simultaneously boosting calorie output - could be the reason why retatrutide has shown greater weight loss results than existing treatments in early clinical trials.
How long does Retatrutide take to work?
In Phase 2 clinical trials, participants began to see measurable weight loss within the first few weeks of treatment. By week 24 (approximately 6 months), the average weight reduction was up to 17.5%, and this continued to increase through to week 48, reaching up to 24.2%.
Notably, participants had not reached a weight loss plateau by the end of the 48-week study, suggesting that the full weight loss potential of retatrutide may extend beyond this timeframe. Longer Phase 3 trials currently underway will help determine the complete efficacy timeline.
Does Retatrutide burn fat?
Yes. Unlike GLP-1-only treatments such as Wegovy, which primarily reduce appetite, retatrutide also directly stimulates fat metabolism through its action on glucagon receptors. Glucagon promotes the breakdown of stored fat (a process called lipolysis) and increases resting energy expenditure, meaning the body burns more calories even at rest. This additional fat-burning mechanism is one of the key reasons retatrutide has demonstrated greater weight loss in clinical trials compared to treatments that target fewer receptors.
How effective is Retatrutide?
In Eli Lilly's Phase 2 clinical trial (published in the New England Journal of Medicine, 2023), 338 adults with obesity or overweight (without diabetes) were treated with retatrutide for 48 weeks. The key findings were:
- Participants receiving the highest dose (12mg weekly) achieved an average weight loss of 24.2% of their body weight by week 48.
- By week 24, average weight loss had already reached 17.5% in the 12mg group.
- Over 90% of participants in the 12mg group lost at least 10% of their body weight.
- Participants had not reached a weight loss plateau at the end of the study, indicating further weight loss may have been possible with continued treatment.
What are Retatrutide side effects?
As with all GLP-1-based treatments, retatrutide can cause side effects. In Phase 2 clinical trials, the safety profile was broadly consistent with other incretin-based therapies, with gastrointestinal side effects being the most commonly reported.
- Nausea - the most common side effect, reported more frequently at higher doses
- Diarrhoea
- Vomiting
- Constipation
- Abdominal pain or discomfort
These side effects were generally mild to moderate in severity and were most common during the dose escalation period (the first 12–16 weeks of treatment, when the dose is gradually increased). Most participants found that symptoms improved or resolved as their body adjusted to the medication.
What is the recommended dose of Retatrutide?
Retatrutide does not yet have a confirmed recommended dose, as it is still in clinical trials. However, the Phase 2 trial investigated several dosing regimens that provide insight into how the treatment may be prescribed once approved.
In the trial, retatrutide was administered as a once-weekly subcutaneous injection at target doses of 1mg, 4mg, 8mg, or 12mg. A dose-escalation approach was used, meaning participants started at a lower dose that was gradually increased over several weeks to reach the target dose. This approach helps minimise gastrointestinal side effects.
How do you take Retatrutide?
Retatrutide is administered as a subcutaneous injection (an injection under the skin) once per week, on the same day each week.
Based on the clinical trial methodology:
- Injection sites: The abdomen, thigh, or upper arm are the recommended injection sites. The injection site should be rotated each week.
- Timing: Retatrutide can be taken at any time of day, with or without food.
- Administration: The treatment is expected to be supplied in a pre-filled injection pen, similar to Mounjaro and Wegovy pens.
Is Retatrutide better than Mounjaro?
Retatrutide and Mounjaro (tirzepatide) both target GLP-1 and GIP receptors, but retatrutide additionally activates glucagon receptors. This third mechanism is thought to enhance fat burning and increase metabolic rate beyond what dual-agonist treatments achieve.
In clinical data to date, retatrutide has shown marginally greater weight loss (~24.2% at 48 weeks in Phase 2) compared to Mounjaro (~22.5% at 72 weeks in Phase 3). However, these results come from different trial stages and designs, making a direct comparison difficult.
Mounjaro is currently MHRA-approved and available through Pharmica, while retatrutide remains in clinical trials. For patients seeking treatment now, Mounjaro represents the most effective approved option, with Pharmica offering it from £159.99 following a free online consultation.
Is Retatrutide better than Semaglutide?
Semaglutide is the active ingredient in Wegovy. While retatrutide has shown greater weight loss in clinical trials (24.2% vs approximately 15–17% for Wegovy), it is important to note that retatrutide targets three hormone receptors, whereas semaglutide targets only one (GLP-1).
The additional receptors allow retatrutide to influence appetite, blood sugar, and fat metabolism through multiple pathways simultaneously, which is believed to account for the difference in efficacy. However, semaglutide has a much longer safety record and is currently the most widely prescribed weight loss injection worldwide.