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Mounjaro and Diarrhoea: What You Need to Know

man suffering with diarrhoea

Mounjaro and Diarrhoea: What You Need to Know

Struggling with diarrhoea after starting Mounjaro (tirzepatide)? You’re not alone, but help is available. Learn what causes it, how to manage it, and when to seek support.

What Is Mounjaro and How Does It Work?

Mounjaro (tirzepatide) is a once-weekly injectable medication used to treat type 2 diabetes and support weight loss. It mimics two hormones: GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide), which help regulate blood sugar levels, slow gastric emptying, and reduce appetite.

Delivered via the easy-to-use KwikPen injection, Mounjaro has quickly become a popular option in the UK for weight management, especially among patients who haven’t responded to other treatments like Ozempic.

Why Does Mounjaro Cause Diarrhoea?

Diarrhoea is one of the most frequently reported gastrointestinal side effects of Mounjaro. Here’s why it happens:

1. Slowed Gastric Emptying

Tirzepatide slows the rate at which your stomach empties, which may disrupt your digestive rhythm, especially in the early weeks.

2. Increased Bile Acid Secretion

GLP-1 and GIP agonists can increase bile production and fluid secretion into the gut, leading to looser stools.

3. Microbiome Shifts

There is some emerging evidence that GLP-1 receptor agonists may alter gut flora, which can affect stool consistency and frequency.

How Common Is Diarrhoea on Mounjaro?

In clinical trials (such as the SURMOUNT-1 and SURPASS studies), diarrhoea was reported in up to 18% of patients taking tirzepatide. Most people experience symptoms in the first few weeks of treatment, especially when moving from 2.5mg to 5mg or 7.5mg doses.

Good news? For many patients, the body adapts, and symptoms often settle within 3 to 5 weeks.

How to Manage Diarrhoea While Using Mounjaro

Hydration Is Key

Drink plenty of fluids to prevent dehydration. Consider using oral rehydration salts (ORS) if symptoms are persistent.

Stick to a Low FODMAP Diet

Avoid foods that ferment quickly in the gut, like onions, garlic, beans, and dairy, at least during flare-ups.

Consider Probiotics

Some patients find relief with live cultures (like Actimel or Yakult) or probiotic supplements.

Timing of Your Injection

Injecting your Mounjaro KwikPen in the evening may help reduce next day symptoms for some patients.

Tip: Always inject into clean skin on your stomach or thigh and rotate sites weekly.

When Should You Be Concerned?

While mild diarrhoea is common, you should speak to a healthcare professional if:

  • It lasts more than 3–5 days

  • You see blood or mucus in your stool

  • You experience severe abdominal pain

  • You feel dizzy, faint, or can’t keep fluids down

At Puri Pharmacy, we offer a complimentary consultation to review your symptoms and determine if a dose adjustment or other interventions are necessary.

Can You Use Anti-Diarrhoeal Medicines With Mounjaro?

Yes, short-term use of loperamide (Imodium) is generally considered safe when used in conjunction with Mounjaro. However, you should avoid prolonged use without medical supervision, especially if the diarrhoea is recurring.

Should I Stop Mounjaro If I Get Diarrhoea?

In most cases, you do not need to stop. Symptoms are usually temporary and manageable. However, if diarrhoea is significantly affecting your quality of life, speak to your pharmacist or prescriber.

We’re happy to offer a private weight loss review and provide tailored advice.

Is It the Dose or the Medication?

Sometimes, diarrhoea can occur after a dose increase. Please discuss with us whether you should stay on your current dose for longer before increasing it.

👉 Book a free consultation with our pharmacist to personalise your treatment plan.

Is It the Injection Pen?

While diarrhoea is not related to the pen delivery itself, some patients report less discomfort when injecting into the abdomen rather than the thigh. Remember: each Mounjaro KwikPen is single-use and prefilled for convenience.

Puri Pharmacy: Your Partner in Weight Loss

We offer:

  • Free initial consultations

  • Weight, BMI, and side effect tracking

  • Medication reviews and prescription adjustments

  • In-store and remote support

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For most patients, diarrhoea tends to be temporary and resolves within 2 to 5 weeks. It’s most common when starting treatment or increasing the dose, particularly from 2.5mg to 5mg or higher doses such as 7.5mg or 10mg.

Yes, loperamide (Imodium) can be used occasionally to manage diarrhoea, but it’s important to avoid using it for more than 48 hours without medical advice. Always check with a pharmacist before taking additional medication alongside your Mounjaro pen injections.

Avoid spicy foods, high-fat meals, dairy, alcohol, and high FODMAP foods like beans, lentils, onions, and garlic. These can all worsen gastrointestinal symptoms. Stick to bland foods like plain rice, bananas, toast, and boiled potatoes during flare-ups.

No. Diarrhoea is a known side effect of GLP-1 and GIP receptor agonists, like Mounjaro (tirzepatide). It usually indicates that your body is adjusting to the medication. If you’re still losing weight and tolerating the medicine well, it doesn’t mean the medication is failing.

Recurring diarrhoea after every Mounjaro injection may indicate a sensitivity to the current dose. Speak to our pharmacist to explore whether:

  • A slower dose escalation is needed

  • Diet adjustments are required

  • You need a temporary dose holding

While there’s no direct evidence that the injection site causes diarrhoea, some patients report fewer gastrointestinal side effects when injecting into the abdomen versus the thigh. Rotating injection sites is still recommended to avoid irritation.

Yes, some patients report IBS style symptoms like cramping, urgency, and loose stools, particularly during the first 1–2 months of treatment. These effects are generally temporary.

You should not stop Mounjaro without professional advice. Most side effects can be managed safely, and stopping prematurely may disrupt your weight loss progress. If diarrhoea is severe or persistent, speak to your prescriber.

You should contact a doctor or pharmacist if:

  • You have bloody or black stools

  • You feel faint, dizzy, or dehydrated

  • Diarrhoea lasts more than 72 hours

  • You’re unable to eat or drink

Severe cases may require blood tests or medical imaging to rule out complications.

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