Mounjaro Side Effects and How to Treat Them

Most people who experience side effects while using Mounjaro (tirzepatide) notice them early in treatment or after a dose increase. In the majority of cases, these effects are mild to moderate, temporary, and improve as the body adapts.

This guide is designed as a troubleshooting playbook. It explains when side effects usually start, how long they last, how to manage specific symptoms at home, and when medical advice is needed.

If you’re looking for a short overview of side effects and eligibility, see the side effects section on our Mounjaro weight loss injections page. For a broader comparison across treatments, you can also view our weight-loss injection side effects guide.

When Do Mounjaro Side Effects Start and How Long Do They Last?

Mounjaro side effects tend to follow a predictable pattern linked to treatment timing and dose changes.

Typical timeline

• First few days: Side effects may begin shortly after starting treatment

• After dose increases: Symptoms may briefly return or intensify

• First 2–4 weeks: Most people notice symptoms easing as the body adapts

• Maintenance dose: Many side effects reduce significantly or resolve

This is why Mounjaro is started at a low dose and increased gradually under clinical supervision.

If symptoms persist
Side effects that last longer than 2–4 weeks, worsen over time, or interfere with eating, drinking, or daily life should be discussed with a prescriber.

At-a-Glance: What’s Normal vs When to Get Help

For urgent concerns contact NHS 111. For emergency symptoms call 999.

Dose Increases: How to Reduce Side-Effect Flare-Ups

It’s common for side effects to reappear briefly when increasing dose.

Before injection day

• Eat lighter meals

• Avoid very fatty or spicy foods

• Ensure good hydration

On injection day

• Keep meals small and simple

• Avoid alcohol

• Eat slowly and stop when full

48–72 hours after increasing

• Focus on fluids, including water or electrolyte drinks

• Choose bland, easy-to-digest foods

• Avoid overeating even if appetite briefly returns

• Reduce strenuous exercise if feeling unwell

What to log for your prescriber

• When symptoms start

• How long they last

• Severity (mild, moderate, severe)

• Whether eating, drinking, or sleep is affected

Your prescriber may advise staying on a lower dose for longer if symptoms are troublesome.

Digestive Side Effects and How to Manage Them

Nausea

Why it happens: Delayed stomach emptying and stronger fullness signals.

Helpful steps

• Smaller, frequent meals

• Bland foods (toast, rice, crackers)

• Sip fluids little and often

• Avoid rich or greasy foods

Seek advice if nausea lasts more than a few days or limits fluid intake.

Vomiting

Why it happens: Strong satiety signals or slowed digestion, particularly after dose increases.

Helpful steps

• Small, frequent meals

• Clear fluids throughout the day

• Stay upright after eating

Persistent vomiting or vomiting with severe pain requires medical advice.

Diarrhoea

Why it happens: Changes in gut motility.

Helpful steps

• Plenty of fluids

• Oral rehydration sachets if needed

• Easy-to-digest foods

• Avoid caffeine and alcohol

Seek advice if diarrhoea lasts longer than 7 days.

Constipation

Why it happens: Reduced food intake and slower digestion.

Helpful steps

• Gradually increase fibre

• Drink plenty of water

• Gentle daily movement

Short-term laxatives may be considered after pharmacy or clinician advice.

Common “Annoying” Mounjaro Side Effects People Often Search For

Some Mounjaro side effects are common but not always discussed in detail. These issues can feel worrying or inconvenient, especially during the first few weeks or after a dose increase, but they often improve as your body adapts. The sections below explain why these symptoms happen and what you can do to manage them safely.

Bloating and Trapped Wind

Why it happens: Food stays in the stomach longer, increasing gas build-up.

Helpful steps

• Eat slowly and chew food well

• Avoid fizzy drinks and drinking through straws

• Gentle walking after meals

• Increase fibre gradually rather than suddenly

Sulphur Burps

Sulphur-smelling burps are caused by hydrogen sulphide gas released during digestion.

Helpful steps

• Smaller, more frequent meals

• Reduce foods high in sulphur (eggs, onions)

• Drink water regularly

• Avoid fizzy drinks

These usually improve as digestion adapts.

Heartburn and Acid Reflux

Slower digestion can increase pressure in the stomach and push acid upwards.

Helpful steps

• Smaller meals

• Staying upright after eating

• Avoiding trigger foods

• Pharmacy-recommended antacids or alginates

For diet-specific support, link here: what to eat while using weight-loss injections.

Fatigue

Often linked to reduced calorie intake, dehydration, or dose increases.

Helpful steps

• Prioritise sleep

• Eat balanced meals with adequate protein

• Stay hydrated

• Gentle activity such as walking

Dizziness or Light-Headedness

May be caused by dehydration, low blood sugar, or blood-pressure changes.

Helpful steps

• Stand up slowly

• Drink fluids regularly

• Eat small, regular meals

• Monitor blood sugar if you have diabetes

Persistent dizziness should be reviewed.

Feeling Cold

Some people feel colder as calorie intake drops and body fat reduces. This is usually harmless and improves over time.

Hair Shedding

Temporary hair shedding can occur during rapid weight loss, rather than as a direct drug effect. This is usually not permanent and often improves once weight stabilises.

Injection-Site Reactions

Mild redness, itching, or tenderness at the injection site is common early on.

To reduce reactions

• Rotate injection sites weekly

• Avoid bruised or irritated skin

• Let the pen reach room temperature before use

• Keep skin clean before injecting

Seek advice if reactions spread, become painful, or are accompanied by swelling elsewhere.

Over-the-Counter Support: What’s Generally Reasonable

Some pharmacy-available products may help manage symptoms. Always follow instructions and seek advice if unsure.

• Electrolyte or oral rehydration sachets for vomiting or diarrhoea

• Antacids or alginates for reflux

• Short-term constipation relief after advice

• Anti-diarrhoeal medicines for short-term use only

Avoid starting new medicines without checking they are suitable alongside Mounjaro.

Mounjaro, Diabetes Medicines and Low Blood Sugar

Low blood sugar (hypoglycaemia) is more likely if Mounjaro is used alongside certain diabetes medicines.

Symptoms may include

• Shaking

• Sweating

• Dizziness

• Confusion

What to do

• Consume a fast-acting sugar source (juice, non-diet fizzy drink, glucose tablets)

• Follow with a longer-acting carbohydrate

• Speak to your prescriber if episodes recur

Severe low blood sugar requires urgent medical attention.

Can I Stop, Pause or Miss a Dose Due to Side Effects?

• Do not stop treatment without medical advice unless symptoms are severe

• Dose increases may be delayed if side effects are troublesome

• If a dose is missed due to side effects, follow prescriber guidance before restarting

If symptoms prevent eating, drinking, or daily functioning, seek medical advice promptly.