Mounjaro Side Effects & Long-Term Management

Mounjaro can affect people in different ways. While many people tolerate it well, some may notice changes as their system adjusts.

Very common side effects (may affect more than 10% of users)

• Nausea
• Diarrhoea
• Vomiting
• Constipation
• Stomach pain

Very common side effects (affecting type 2 diabetics taking antidiabetic medication)

Very common side effects can occur in people with type 2 diabetes who are taking Mounjaro alongside other antidiabetic medications.

These effects are usually related to how the body adjusts to changes in blood sugar and the way the medicines work together.

• Low blood sugar levels
• Headache
• Drowsiness
• Weakness
• Dizziness
• Feeling hungry
• Confusion
• Irritability
• Fast heartbeat

Common side effects (May affect up to 10% of users)

• Allergic reaction (rash, itching, eczema)
• Dizziness
• Low blood pressure
• Decreased appetite
• Indigestion
• Bloating
• Burping
• Gas
• Reflux or heartburn
• Hair loss
• Feeling tired
• Injection site reaction
• Fast pulse

Side effects usually subside after a few days. Most side effects show up after a dose increase and typically ease as your body adjusts to the dose.

If you stop taking Mounjaro, the side effects will go away.

Mounjaro side effects usually begin within a few days of starting treatment or increasing the dose.

Starting dose (2.5mg) & each dose increase (every 4 weeks):
This is when tummy symptoms like nausea, vomiting, diarrhoea and constipation are most likely. They’re usually mild to moderate and tend to settle once you stay on the same dose for a bit.

After you reach a steady “maintenance” dose (often 10–15 mg):
Side effects generally drop off. Many people have little to none at this stage.

Sometimes, yes – temporarily. The stomach-related effects are most likely to flare up when you increase the dose, then usually settle again once you stay at that level for a few weeks.

Not everyone gets worse, and many people have little or no change.

This happens because the higher doses amplify the same gut-hormone effects such as slower stomach emptying and reduced appetite. Your body typically adapts with time.

In a large weight-loss study called SURMOUNT-1, which is a clinical trial where researchers test a medication to see how well it works and how safe it is, a small number of people stopped taking Mounjaro because they experienced side effects. They stopped at around:

• 4.3% on 5mg
• 7.1% on 10mg
• 6.2% on 15mg
• vs 2.6% on placebo

Most drop-outs happened early during dose increases.

Specifically for stomach (GI) issues, stopping due to GI side effects were at:

• 1.9% on 5mg
• 3.3% on 10mg
• 4.3% on 15mg
• vs 0.5% on placebo

Over the longest studies so far which were up to 3 years, researchers haven’t found any long-term side effects or problems beyond what we already know, mostly stomach related.

The known, uncommon but important risks remain the same and are monitored.

What we know from longer-term research

• Up to 3 years of follow-up: No new safety concerns were found. The side-effect pattern stayed the same as earlier studies. Most issues were gastrointestinal including nausea, diarrhoea and vomiting and tended to be mild-moderate, mainly appearing when the dose was increased.
• Staying on treatment: In the 72-week obesity study, about 4-7% of people taking tirzepatide stopped because of side effects (compared to around 3% on placebo). Most people who stopped did so early on while their dose was increasing.

Pancreatitis

• How common: Up to 0.2% of users
• Why it can happen: Exact cause isn’t clear.
• What to watch for: Severe, persistent upper-abdominal pain, which may spread to the back, often with vomiting. Stop the medicine and seek urgent medical care/A&E.

Gallbladder problems (gallstones, gallbladder inflammation)

• How common: Up to 1% of users
• Why it can happen: Fast weight loss changes bile flow → gallstone formation.
• What to watch for: Sharp pain under right ribs, fever, nausea/vomiting, yellowing of skin/eyes. Contact a clinician urgently or go to A&E.

Acute kidney injury

• How common: Up to 0.5% of users
• Why it can happen: Dehydration from GI upset reduces kidney perfusion.
• What to watch for: Can’t keep fluids down, dizziness, very dark urine, reduced urination.

Severe allergic reaction (anaphylaxis/angioedema)

• How common: Up to 0.1% of users
• Why it can happen: Immune reaction to the drug/excipients.
• What to watch for: Swelling of face/lips/tongue, hives, wheezing, collapse.

*If you experience any of the above symptoms, you should seek urgent medical attention.

Diarrhoea

How many people does it affect: Up to 23% of users. Most cases appear during dose increases and ease with time.

Why it happens: Mounjaro slows and alters gut movement and stomach emptying, which can change how your intestines handle food and fluids, especially when your appetite and portion sizes are shifting.

What to do:

• Sip fluids regularly; add oral rehydration if stools are frequent
• Go lighter on fatty/spicy foods; consider smaller, simpler meals for a few days
• Avoid sugar alcohols (e.g., sorbitol) and heavy caffeine
• If persistent, ask your clinician about short-term loperamide and whether to pause/increase the dose more slowly.

Nausea (Feeling sick)

How many people does it affect: Up to 33% of users; usually mild–moderate and improves after a few weeks at a steady dose.

Why it happens: Mounjaro delays gastric emptying and reduces appetite; a “full” feeling can trigger queasiness during dose steps.

What helps:

• Small, low-fat meals; avoid big portions, especially on injection day
• Ginger/peppermint, regular hydration, slow eating
• If needed, ask about a short course of anti-nausea medication or raising the dose at a slower pace

Vomiting

How many people does it affect: Up to 13% of users; peaks during a dose increase then subsides.

Why it happens: Slower stomach emptying plus large/fatty meals can overwhelm the stomach early on

What helps:

• Pause eating briefly; re-introduce sips of water/electrolytes
• Stick to light foods (e.g., toast, rice) for 24-48h
• Speak to your clinician about anti-emetics and holding the dose increase; seek help urgently if you cannot keep fluids down

Constipation

How many people does it affect: Up to 17% of users; peaks during a dose increase then subsides.

Why it happens: Slowed stomach emptying together with smaller, low-fat meals can reduce natural stool-stimulating signals.

What helps:

• Fluids and fibre (wholegrains, vegetables; add psyllium if needed)
• Move daily (even short walks)
• Consider an osmotic laxative (e.g., macrogol) short-term after checking with your clinician
• If ongoing, ask about moving up to the next dose more gradually

Bloated stomach

How many people does it affect: Up to 4% of users.

Why it happens: Slower gastric emptying and more gas from dietary changes can cause fullness/bloat, especially early on.

What helps:

• Smaller meals; avoid carbonated drinks/beans for a few days.
• Gentle walking after meals; try peppermint tea or simethicone.
• Rule out constipation or reflux – treat those and bloat often settles

Sulphur burps

How many people does it affect: Up to 5% of users.

Why it happens: Slowed stomach emptying can lead to gas build-up; certain foods (e.g., eggs, onions, broccoli) release sulphur gases that smell like “rotten eggs.” Reflux can make burps more noticeable.

What helps:

• Temporarily cut-back on high-sulphur foods and carbonated drinks
• Eat slowly, avoid lying flat after meals
• If reflux dominates, ask your doctor about acid-suppressing medication such as omeprazole
• Ask about slower dose steps if burps are persistent

Headache and dizziness

How many people does it affect: Up to 5% of users.

Why it happens: Often dehydration, meal pattern changes, caffeine swings, or if you have diabetes, glucose changes during early weight loss.

What helps:

• Hydrate; don’t skip meals.
• Keep caffeine steady day-to-day.
• If you have diabetes, check glucose when headaches hit.
• Simple analgesia (e.g., paracetamol) if appropriate; speak to your clinician if persistent/worsening.

Tiredness and fatigue

How many people does it affect: Up to 7% of users.

Why it happens: Early calorie deficit, rapid weight loss, dehydration, and sleep changes can all contribute while your body adapts.

What helps:

• Prioritise protein, fluids, and regular meals.
• Keep electrolytes up if you’ve had GI upset.
• Aim for consistent sleep and light daily activity.
• Ask about holding/slowing the next dose step if fatigue is marked.

Most Mounjaro (tirzepatide) side effects are mild, short-lived, and happen during dose increases, then settle once you’re on a steady dose.  

Serious problems are uncommon, and only a small percentage of people stop treatment because of side effects.  

If you plan by starting low, go slow, stay hydrated, choose smaller/low-fat meals, add fibre, and speak to your clinician about pausing the next dose step if needed, you’ll maximise results while minimising nausea, diarrhoea, constipation, vomiting, and bloating. 

If you notice severe or persistent upper-abdominal pain, fever/jaundice, or you cannot keep fluids down, seek urgent medical help.