What is Retatrutide?: The New Triple G Weight Loss Drug

• Updated on: August 5, 2025

The world of weight loss medications is evolving rapidly, and retatrutide is making headlines as one of the most promising new treatments. Known as the “triple G” obesity drug, retatrutide works differently from existing weight loss injections by targeting not just one, but three important hormone pathways in your body.

While medications like Mounjaro and Wegovy have already transformed weight loss treatment, retatrutide could be the next game-changer. Early clinical trials suggest it might help people lose even more weight than current options, though it’s still being tested and isn’t yet available to the public.

How does retatrutide work?

Retatrutide is called a ‘triple G’ drug because it targets three different hormone receptors at the same time: GLP-1, GIP, and glucagon. This triple action is what sets it apart from other weight loss medications currently available:

GLP-1 (glucagon-like peptide-1) Receptor Agonist

This is the same hormone targeted by medications like Ozempic and Wegovy, and it helps you feel full after eating and slows down how quickly food leaves your stomach. It also helps regulate blood sugar levels.

GIP (glucose-dependent insulinotropic polypeptide) Receptor Agonist

Mounjaro also targets the hormone alongside GLP-1, which helps with feeling full and blood sugar control, but it works slightly differently from GLP-1. It’s particularly good at helping your body respond better to insulin.

Glucagon Receptor Agonist

This is the new addition that makes retatrutide unique. Glucagon normally tells your liver to release stored sugar, but when blocked in a controlled way, it can help increase your metabolism and encourage your body to burn more fat.

How much weight can I lose on retatrutide?: Clinical Trials & Weight Loss Results

The weight loss results from retatrutide clinical trials have been impressive, though it’s important to remember these are still early-stage studies with relatively small groups of participants.

The phase 2 trial followed participants for 48 weeks (nearly a year). People taking the highest dose of retatrutide lost an average of 24% of their starting body weight – that’s nearly a quarter of their total weight.

To put this in perspective, if someone weighed 100kg (about 15.7 stone) at the start, they could potentially lose around 24kg (nearly 4 stone) on average.

What are the side effects of retatrutide?

Since retatrutide is still in clinical trials, we don’t have complete information about all possible side effects yet. However, based on the studies conducted so far, the side effects appear similar to other weight loss injections, but potentially more intense due to its triple action.

The most common side effects reported in trials include:

Digestive issues

• Nausea (the most frequently reported side effect)
• Vomiting
• Diarrhoea
• Constipation
• Stomach pain or discomfort
• Loss of appetite

Other reported effects

• Fatigue or tiredness
• Injection site reactions (redness, swelling, or irritation)

Most side effects tend to be worse when starting the medication or increasing the dose, and often improve as your body adjusts. In clinical trials, many people found that starting with a lower dose and gradually increasing it helped reduce these effects.

It’s worth noting that because retatrutide targets three hormone pathways instead of one or two, some people in trials experienced more pronounced digestive side effects compared to other weight loss medications. But this will be different from person to person.

Who can use retratrutide?

Since retatrutide is still in clinical trials and not yet approved for public use, we can only discuss the criteria used in current studies and what might be expected when it becomes available.

In the clinical studies so far, participants have generally needed to meet these requirements:

• BMI of 30 or above (classified as obese), or BMI of 27 or above with weight-related health conditions like type 2 diabetes, high blood pressure or dyslipidemia 
• Adults aged 18 and over
• No history of certain medical conditions like pancreatitis or severe kidney disease
• Not pregnant or breastfeeding

What is the dosing schedule of retratrutide, and how is it administered?

In clinical trials, retatrutide has been given as a weekly injection under the skin (subcutaneous). It will likely be sold as a pre-filled injectable pen, similar to other weight loss injections.

Starting with a low dose and gradually increasing over several weeks, the typical starting dosage is around 1mg per week, potentially increasing to 12 mg per week.

The gradual dose increase helps reduce side effects, particularly the common digestive issue, when starting treatment.

Is retatrutide better than other weight loss injections?

While the early results from retatrutide trials look promising, direct head-to-head comparisons haven’t been done yet. What we can do is look at the separate trial results and see how they stack up.

Based on the clinical trial data available, retatrutide appears to offer superior weight loss compared to existing options. In trials, people taking retatrutide lost an average of 24% of their body weight over 48 weeks, compared to around 15-17% with Wegovy (semaglutide) and 15-22% with Mounjaro (tirzepatide). 

Because retatrutide targets three hormone pathways instead of one or two, some people in trials experienced more pronounced side effects, particularly digestive issues like nausea and vomiting.

When it comes to convenience, retatrutide would likely be similar to existing weight loss injections – a once-weekly injection that you can do at home. The gradual dose escalation approach used in trials also mirrors what we see with Wegovy and Mounjaro, helping to minimise initial side effects.

Is retatrutide available to buy in the UK?

Retatrutide is not currently available to buy anywhere in the UK. The medication is still in phase 3 clinical trials for weight reduction and hasn’t been approved by any regulatory authority, including the MHRA (Medicines and Healthcare Products Regulatory Agency) in the UK.

The drug is being developed by Eli Lilly, the same company behind Mounjaro, but it’s still several years away from potentially reaching the weight management market. Current trials are focusing on proving the medication’s safety and effectiveness before it can be considered for approval in the UK.

If you’re looking for weight loss medications that are currently available, options like Wegovy, Mounjaro, and Saxenda are already licensed and can be prescribed in the UK. At Click2Pharmacy, we can help you access these proven weight loss treatments through our online weight loss clinic, where you can have an online consultation with qualified healthcare professionals.