Retatrutide Side Effects

The most common side effects of retatrutide are stomach and digestive symptoms. These include:

• nausea
• vomiting
• diarrhoea
• constipation
• bloating
• burping
• indigestion
• stomach pain or discomfort
• feeling full quickly after eating

These symptoms happen because retatrutide affects gut hormone pathways involved in appetite, digestion and weight regulation. It may slow stomach emptying and reduce appetite, which can make some people feel sick, bloated or uncomfortable after eating.

Retatrutide is still investigational and is not currently licensed by the MHRA for weight loss in the UK. (Further reading: Where to buy retatrutide in the UK)

In the TRIUMPH-1 Phase 3 trial, the most common retatrutide side effects were nausea, diarrhoea, constipation and vomiting.

Retatrutide side effects can start on day 1, but they do not always happen immediately.

Some people may notice nausea, bloating, burping or appetite changes within the first 24 to 48 hours after an injection. Others may develop symptoms gradually over the first few weeks.

Side effects are more likely to start or worsen:

• after the first dose
• after a dose increase
• after eating a large meal
• after fatty, greasy or spicy food
• when reaching a higher dose

Retatrutide side effects may last a few days, several weeks or longer.

Digestive side effects such as nausea, diarrhoea, constipation and vomiting are often worse when treatment starts or after a dose increase. They may improve as the body adjusts, but some people may continue to experience symptoms at higher doses.

Severe, persistent or worsening side effects should not be ignored. Anyone who has used an unlicensed product labelled as retatrutide should seek medical advice if they feel unwell.

Further reading: Retatrutide dosage

The long-term side effects of retatrutide are not fully known yet because the medicine is still being studied and has not been approved for routine use in the UK.

So far, the most common side effects seen in clinical trials have been digestive symptoms, such as nausea, vomiting, diarrhoea, constipation, bloating, burping and indigestion. These are usually more noticeable when treatment starts or when the dose is increased.

Long-term safety monitoring is still important because retatrutide may cause significant weight loss and affects several hormone pathways. Areas that need further study include:

• gallbladder problems, especially with rapid weight loss
• pancreatitis, which is inflammation of the pancreas
• changes in resting heart rate
• thyroid safety
• liver safety, especially with unregulated online products
• muscle loss during rapid weight loss
• nutritional deficiencies if food intake becomes too low
• longer-term digestive symptoms

There is currently no confirmed evidence that retatrutide causes cancer in humans, but its long-term cancer safety profile has not yet been fully established.

Because retatrutide is not licensed in the UK, it should not be bought online or used outside an authorised clinical trial. Anyone using an unregulated product labelled as retatrutide should seek medical advice if they experience severe or persistent symptoms.

Nausea is one of the most common retatrutide side effects.

In Phase 3 trials, nausea affected up to 42.4% of people taking retatrutide, depending on the dose. It was more common at higher doses.

Retatrutide nausea may feel like:

• feeling sick
• queasiness after eating
• reduced appetite
• early fullness
• food aversion
• an unsettled stomach

Nausea is more likely during the first few weeks, after a dose increase, or after eating large, greasy, fried, spicy or very sweet foods.

Vomiting can happen with retatrutide, especially at higher doses or after dose increases.

In Phase 3 trials, vomiting affected up to 25.3% of people taking retatrutide, compared with 4.8% on placebo.

Vomiting should be taken seriously if it is severe, persistent, or stops you from keeping fluids down. Repeated vomiting can lead to dehydration, dizziness, weakness and kidney strain.

Seek medical advice urgently if vomiting is severe, does not settle, or happens with severe abdominal pain, fainting, confusion, blood in vomit or signs of dehydration.

Diarrhoea is a common retatrutide side effect.

In Phase 3 trials, diarrhoea affected up to 34.1% of people taking retatrutide, compared with 13.5% on placebo.

Retatrutide diarrhoea may be more likely when treatment starts, after a dose increase, or after eating foods that are harder to digest. Fatty meals, alcohol, large portions and rich foods may make diarrhoea worse.

Seek medical advice if diarrhoea is severe, lasts for more than a few days, causes dehydration, or happens with blood, fever or severe abdominal pain.

Constipation is also common with retatrutide.

In Phase 3 trials, constipation affected up to 26.1% of people taking retatrutide, compared with 10.9% on placebo.

Constipation may happen because retatrutide can reduce appetite, reduce food intake and slow digestion. People may also drink less fluid if they are eating less, which can make constipation worse.

Constipation may feel like:

• passing stools less often
• hard or dry stools
• straining
• bloating
• abdominal discomfort
• feeling that the bowel has not fully emptied

Retatrutide may cause bloating, burping, trapped wind, reflux or indigestion.

These symptoms may happen because food can remain in the stomach for longer. Some people may feel full quickly, feel bloated after eating, or notice more burping than usual.

Bloating and burping may be worse:

• after eating
• after large meals
• after fatty or fried foods
• after fizzy drinks
• when eating quickly
• when lying down soon after food

Smaller, simpler meals are usually easier to tolerate than large, heavy meals.

Some people may feel worse after eating while taking retatrutide. This may include nausea, bloating, burping, reflux, stomach pain, diarrhoea or vomiting.

This is more likely after:

• large meals
• greasy or fried foods
• spicy foods
• very sweet foods
• fizzy drinks
• alcohol
• eating too quickly
• lying down soon after meals

If retatrutide is approved in the future, patients are likely to need dietary guidance to help manage digestive side effects safely.

Hair loss has not been established as a common side effect of retatrutide in clinical trials. However, rapid weight loss itself can sometimes trigger temporary shedding, known as telogen effluvium.

This type of hair loss can happen when the body goes through a significant physical change, including rapid weight loss, reduced calorie intake, low protein intake or nutritional deficiencies.

If retatrutide is approved in the future, patients losing weight quickly may need advice on protein intake, nutrition and safe weight loss monitoring. Anyone experiencing sudden, patchy or severe hair loss should speak to a healthcare professional.

Retatrutide has been linked with increases in resting heart rate in clinical trials. In the Phase 2 obesity trial, heart-rate increases were dose-dependent, peaked around 24 weeks and then declined afterwards.

A small increase in resting heart rate does not necessarily mean retatrutide causes serious heart problems, but heart safety is still being monitored because the medicine is investigational.

Seek medical advice urgently if you experience chest pain, fainting, severe dizziness, shortness of breath, or a fast or irregular heartbeat.

There is currently no confirmed evidence that retatrutide causes cancer in humans. However, retatrutide is still investigational, so its long-term cancer safety profile has not yet been fully established.

The main cancer concern discussed with medicines in this area is thyroid cancer, particularly medullary thyroid cancer. This warning is based mainly on findings seen with some incretin-based medicines in animal studies, rather than confirmed human cases.

Because retatrutide is not currently approved in the UK, the final cancer warnings, contraindications and safety guidance will only be confirmed if the medicine is reviewed and licensed by regulators.

Anyone with a personal or family history of medullary thyroid cancer, thyroid nodules, MEN2, or unexplained neck swelling should speak to a healthcare professional and avoid unregulated products sold online.

Retatrutide is not approved in the UK, so there is no official patient guidance yet. However, in clinical practice with similar weight loss medicines, digestive symptoms are often managed by reducing triggers and keeping meals simple.

The most common retatrutide side effects are nausea, diarrhoea, constipation, vomiting, bloating, burping and indigestion. These symptoms are more likely when treatment starts, after a dose increase, or after eating large, fatty or rich meals.

In Phase 3 trials, nausea affected up to 42.4% of people, diarrhoea up to 34.1%, constipation up to 26.1%, and vomiting up to 25.3%, depending on the dose.

Retatrutide is not currently approved in the UK and should not be bought online or used outside an authorised clinical trial.