What is Retatrutide?

Retatrutide is a triple agonist, which means it targets the receptors of the following 3 hormones to mimic their effects, resulting in improved blood sugar levels and weight loss:

1. Glucagon-like peptide-1 (GLP-1) – stimulates the release of insulin (an essential hormone for managing blood sugar), slows down how long it takes for food to pass through the stomach, and suppresses your appetite.
2. Glucose-dependent insulinotropic polypeptide (GIP) – increases the amount of insulin released by the pancreas to reduce blood sugar levels and lower appetite levels.
3. Glucagon – a hormone naturally produced by the pancreas to regulate blood sugar levels and break down fat more effectively into fatty acids, so it can be used for energy.

By mimicking the effects of these 3 hormones, retatrutide can help you lose weight by suppressing your appetite, increasing fat metabolism, and increasing insulin sensitivity.

How long does retatrutide last?

Like Mounjaro and Wegovy, retatrutide will be a once-weekly injection and studies show it has a half-life of around 6 days, which is how long it takes for half of the active ingredient to leave your body. So, to maintain its effectiveness, it will need to be injected on the same day every week.

How long does retatrutide take to work?

Retatrutide starts to work after the first injection, but it can take several weeks to notice the full effects. Studies have shown that you can lose up to 17.3% on 4mg at 24 weeks of treatment.

How effective is retatrutide?

Phase 2 clinical trials have shown some promising results, with the highest weekly dose of 12mg causing an average weight loss of 24.2% after 48 weeks. Within this group, more than a quarter (26%) lost at least 30% of their initial body weight.

Even a lower dose of 4mg per week of retatrutide helped people lose more than 17% of their body weight in 48 weeks. It also resulted in:

• 92% losing at least 5% of their starting weight
• 75% losing at least 10% of their starting weight
• 60% losing at least 15% of their starting body weight

The same study also showed promising results for type 2 diabetes, with 72% of participants who had prediabetes reporting normal blood sugar levels after 48 weeks compared to 22% on placebo.

Retatrutide also improved several cardiovascular (conditions affecting your heart and blood vessels) and also improved other measures for monitoring heart diseases and diabetes, including:

• blood pressure
• blood fats
• insulin levels
• fasting blood glucose

Retatrutide is still in phase 3 clinical trials, which are assessing its effectiveness for obesity. The final results from these trials should be available in 2026.

Retatrutide will be a once-weekly self-injectable medication, similar to other GLP-1 agonists. Exactly how it will be taken and the dosage schedule have not been released yet because it's still in the testing phase. However, looking at how similar medications are taken, you will likely begin on a low dose and gradually increase (titrate) the dose until you reach the maximum maintenance dose. This allows the body to get used to the medication and reduces the chance of side effects, which is common practice with GLP-1 weight loss medications.

Other once-weekly injections like Mounjaro come in the form of an injectable pen with pre-filled doses that you inject yourself at home, so the manufacturer will likely do the same with retatrutide.

At present, there is no official dosage schedule for retatrutide. However, in clinical trials, retatrutide was started at a low dose and gradually increased over several weeks, similar to other weight loss medications.

In the phase 2 clinical trial, the participants were assigned to groups, and 5 different doses were tested: 1, 2, 4, 8, or 12mg. The retatrutide dosage schedule in this study was:

• starting dose – 1 or 2mg per week
• maximum dose – up to 12mg per week
• maintenance dose – 4 to 12mg, depending on which study group the participant was in
• dose escalation – 4-weekly

Retatrutide is not available and is unlikely to be available before 2027, as it is still undergoing phase 3 clinical trials. It has not been approved by any regulatory agency in the world, including the Food and Drug Administration (FDA) in the US or the Medicines and Healthcare products Regulatory Agency (MHRA) in the UK.

Phase 3 trials are scheduled to finish in May 2026. After this, the data will be used to support an application for use in the US, and possibly the UK, either in 2026 or 2027. It can take several months for a medication to be approved and another several months to be produced.

Will it be prescription only?

Yes, like other GLP-1 agonists, retatrutide will be a prescription-only medication, so it will not be available over the counter, and you will need a doctor’s approval to obtain it.

Retatrutide has similar side effects to Mounjaro and Wegovy, with mild to moderate gastrointestinal symptoms being the most commonly reported, such as:

• feeling or being sick (nausea or vomiting)
• diarrhoea
• constipation

These side effects are more likely to occur when you first start treatment or when the dose increases. Long-term safety data is currently limited. A full list of side effects will be available once the medication has finished testing phases and is submitted for approval.

A few more serious side effects were also noted during clinical trials. However, further research is needed to check whether this is caused by the medication or other factors. This includes:

• allergic reactions to the medication (hypersensitivity)
• trial patient personal bodily or immune system reaction to the medication during treatment
• increased sensitivity to the senses (hyperesthesia)
• heart rhythm problems (cardiac arrhythmia)
• liver disease
• biliary disorders, such as cholecystitis or cholelithiasis, which affect the bile ducts and gallbladder
• kidney problems
• pancreatitis

What to do if you get retatrutide side effects

Most of the commonly reported side effects of retatrutide are mild and can be managed at home by:

• getting plenty of rest until you feel better
• eating smaller, more frequent meals
• avoiding spicy, greasy, and fatty foods
• eating plain, bland foods, like crackers and plain toast
• drinking ginger, peppermint, or chamomile tea
• staying hydrated
• taking over-the-counter remedies, such as painkillers or anti-diarrhoea medications (you should speak to your doctor or pharmacist first)

If you experience any of the following severe side effects, you should get urgent medical attention or call 999 in the case of an emergency:

• breathing or swallowing difficulties
• swelling of the face, lips, tongue, or throat
• severe stomach pain
• loss of consciousness

Emerging research suggests that retatrutide is more effective for weight loss than Mounjaro and Wegovy, with people losing a greater amount of weight, on average, and in a shorter period of time. Retatrutide acts on 3 hormone receptors, while Mounjaro acts on 2, and Wegovy targets 1, which could explain the advanced effectiveness.

Retatrutide vs Mounjaro

Mounjaro contains the active ingredient, tirzepatide, which is a different medication from retatrutide. Mounjaro targets the GLP-1 and GIP receptors, whereas retatrutide targets both of these plus glucagon receptors. In clinical trials, at the highest dose, Mounjaro had an average weight loss of 22.5% of starting body weight after 72 weeks, whereas the average weight loss with 12mg of retatrutide is 24.2% after just 48 weeks.

Retatrutide vs Wegovy

Wegovy contains semaglutide, a GLP-1 receptor agonist, which works by suppressing your appetite and slowing digestion. Retatrutide also targets GIP and glucagon receptors to increase its effects. At the highest dose (2.4mg), Wegovy can support an average weight loss of 17% over 68 weeks.

The same study found that 83.5% of people receiving the highest dose of Wegovy lost at least 5% of their starting body weight, compared to 100% of those given the highest dose of retatrutide.

• Mounjaro KwikPen 2.5mg solution for injection in pre-filled pen, emc [accessed 21 October 2025]
• Obesity, NHS [accessed 21 October 2025]
• Once-Weekly Semaglutide in Adults with Overweight or Obesity, NEJM [accessed 21 October 2025]
• Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial, NEJM [accessed 20 October 2025]
• Wegovy 2.4 mg, FlexTouch solution for injection in pre-filled pen, emc [accessed 21 October 2025]