Diarrhoea on Mounjaro or Wegovy

Side Effects, Causes & What Helps (UK GP Guide)

Quick summary

• Diarrhoea is a recognised side effect of GLP-1 medications like Mounjaro and Wegovy

• It’s often mild and more common when starting or increasing the dose

• Hydration, diet changes, and short-term treatments can help

• Most cases settle, but red flag symptoms should not be ignored

• Ongoing symptoms may benefit from a personalised medication review

What is diarrhoea?

Diarrhoea usually means passing three or more loose or watery stools in a day, or going more often than is normal for you.

It happens when:

• Too much fluid is drawn into the bowel

• Stool moves too quickly for water to be absorbed

• The gut lining becomes irritated or inflamed

It’s very common and, in most cases, short-lived—but it can be disruptive, particularly if it’s linked to medication.

Common causes of diarrhoea

In general practice, the most frequent causes include:

• Viral infections (“stomach bugs”)

• Food poisoning (bacterial infections)

• IBS-D (irritable bowel syndrome with diarrhoea)

• Medications (including antibiotics and weight loss injections like Mounjaro and Wegovy)

• Food intolerances (e.g. lactose)

• Stress and hormonal changes

Medications are an important and often overlooked trigger. Common examples include antibiotics, metformin, anti-inflammatories (like ibuprofen), and some blood pressure or mental health medications.

Can Mounjaro or Wegovy cause diarrhoea?

Yes—although constipation is more commonly discussed, diarrhoea is a recognised side effect of both Mounjaro (tirzepatide) and Wegovy (semaglutide).

As a GP, I’m seeing this more frequently with the rise in GLP-1 use for weight loss.

These medications work by slowing gastric emptying and altering how the gut processes food. During this adjustment—particularly when starting treatment or increasing the dose—some people experience:

• Loose stools

• Urgency

• Intermittent diarrhoea

For most patients, these symptoms are temporary and improve as the body adapts. However, for some, they can persist and become frustrating to manage.

Why it can be difficult to manage

One of the challenges is that treatment options can feel limited.

Advice usually focuses on:

• Staying well hydrated

• Adjusting diet

• Allowing time for the body to adapt

While this is often enough, it doesn’t always fully control symptoms—especially in those with IBS-D or medication-related diarrhoea.

What helps diarrhoea? Practical steps

For mild to moderate symptoms, the following can make a real difference:

1. Hydration

• Drink plenty of fluids

• Consider oral rehydration solutions if symptoms are more significant

2. Adjust your diet temporarily

• Avoid caffeine, alcohol, and artificial sweeteners

• Stick to simple, bland foods while symptoms settle

3. Identify triggers

• Review recent diet changes

• Consider whether symptoms relate to medication timing or dose increases

4. Short-term medications

• Over-the-counter treatments such as loperamide (e.g. Imodium) can reduce stool frequency in the short term

5. Gut-targeted approaches

Some patients prefer options that work directly within the gut.

One example is Enterosgel, an oral intestinal adsorbent available over the counter in the UK.

It works by binding to unwanted substances such as toxins and bacteria in the gut, helping remove them through the stool.

• It is not absorbed into the bloodstream

• It is generally well tolerated

• It can be used for short-term diarrhoea, including IBS-D or medication-related symptoms

As with any treatment, it’s sensible to check suitability with a pharmacist or GP—particularly if you are pregnant, have underlying conditions, or take regular medications.

When should you see a doctor?

Diarrhoea is usually mild, but it’s important to recognise when to seek medical advice.

Seek urgent help if you have:

• Signs of dehydration (dry mouth, passing less urine, dizziness, confusion)

• Fever

• Blood in your stool

• Severe abdominal pain

Arrange a GP review if you have:

• Symptoms lasting more than 5–7 days

• Unexplained weight loss

• Persistent change in bowel habit

• Iron deficiency anaemia

• Rectal bleeding

• A persistent abdominal mass

These symptoms may indicate a more serious underlying cause and should not be ignored.

When to review your Mounjaro or Wegovy treatment

If diarrhoea is ongoing or affecting your quality of life, it may be worth reviewing your treatment plan.

In some cases, simple adjustments can help:

• Slower dose escalation

• Dose reduction

• Dietary optimisation alongside treatment

A personalised review can often make a significant difference without needing to stop the medication altogether.

Summary

Diarrhoea is a common issue and, for many people, it will settle on its own.

However, with the increasing use of medications like Mounjaro and Wegovy, we’re seeing more patients with medication-related gut side effects.

For most, simple measures such as hydration, diet changes, and short-term treatments are enough. In others, additional support or a medication review may be helpful.

If your symptoms are persistent, severe, or accompanied by warning signs, it’s important to seek medical advice.

If you’re unsure whether your symptoms are related to your medication—or you’re struggling to manage side effects—getting tailored advice can help you stay on track safely.

FAQs

Can Mounjaro or Wegovy cause diarrhoea?

Yes. While constipation is more common, some patients experience diarrhoea, particularly when starting treatment or increasing the dose.

How long does diarrhoea last on Mounjaro or Wegovy?

For many people, it settles within a few days to weeks as the body adjusts. Persistent symptoms should be reviewed.

Should I stop Mounjaro or Wegovy if I have diarrhoea?

Not necessarily. Mild symptoms can often be managed, but more severe or ongoing issues should be discussed with a GP.

What is the best diarrhoea treatment in the UK?

Treatment depends on the cause but usually includes hydration, dietary adjustments, and short-term medications. Some people also consider gut-targeted options such as intestinal adsorbents such as Enterosgel.

What helps IBS-D symptoms quickly?

Managing triggers (diet, stress), using short-term treatments, and supporting gut function can all help reduce symptoms.