All conditions
Delivery & Returns
FAQs
Live Chat

Email

Customer Service Team available now: Mon-Fri 8:00-17:00

Close ×

Mounjaro side effects explained

A doctor’s cohesive guide to safety

Medically reviewed by Dr. Allyson Betts Written by Dr. Caroline Fontana Last reviewed 16-07-2026

Time to read: 11 min

Mounjaro is a highly effective weight loss treatment, but it does come with potential side effects. In this guide, I break down the side effects, from the common to the rare and serious, and provide my expert advice on how best to manage them.

With all the information in this guide, I hope to give you all you need to take Mounjaro safely and effectively.

Information on this page

Key takeaways
Side effect frequency: what the rankings mean
Side effects of Mounjaro
At what point do side effects usually start?
How long do Mounjaro side effects last for?
When to contact a doctor
Managing side effects: a doctor’s expert tips
The bottom line

Key takeaways

The most common Mounjaro side effects are gastrointestinal (nausea, vomiting, diarrhoea, constipation) and are generally mild and temporary.
Side effects are ranked by frequency, with 'Very Common' affecting more than 1 in 10 people, and 'Uncommon' affecting up to 1 in 100 people.
Serious, but rare, side effects include acute pancreatitis and severe allergic reactions, which require immediate medical attention.
Side effects often start within the first few days of treatment and usually resolve within a few weeks as the body adjusts.
Ways to manage common side effects include dietary changes and proper injection technique. If side effects persist, see a doctor.

Side effect frequency: what the rankings mean

Before I go into the side effects themselves, I first want to briefly explain the standardised ranking system for side effects used by the European Medicines Agency (EMA). This will give you a better idea of what to expect when taking Mounjaro in regards to side effects.

Side effect ranking	How many people it affects	Percentage chance
Very common	More than 1 in 10	10% or higher
Common	1 in 10 - 1 in 100	1% - 10%
Uncommon	1 in 100 - 1 in 1,000	0.1% - 1%
Rare	1 in 1,000 - 1 in 10,000	0.01 - 0.1%
Very rare	Less than 1 in 10,000	Less than 0.01%

Side effects of Mounjaro

Mounjaro side effects vary widely in frequency and intensity. Some are more common and nothing to worry too much about, while others are rare and potentially severe. Here are all the listed side effects of Mounjaro, starting with the most common ones and ending with rarer, more serious ones.

Very common side effects

The following very common side effects affect more than 1 in 10 people:

Low blood sugar*
Nausea
Diarrhoea

Vomiting
Stomach pain
Constipation

*In people taking medicine for type 2 diabetes

Since Mounjaro works mainly in the gut and digestive system, the most common side effects are gastrointestinal. While this can be uncomfortable at first, most patients find it only lasts for a few days while their body gets used to the medicine.

Low blood sugar is also a very common side effect in people who have type 2 diabetes and are also taking insulin. If this is the case, you may be prescribed a lower dose of your other medication while taking Mounjaro to control blood sugar levels.

Common side effects

The following common side effects affect up to 1 in 10 people:

Allergic reaction
Dizziness
Low blood pressure
Indigestion
Bloating
Gas (flatulence)

Acid reflux/heartburn
Hair loss
Injection site reactions
Fast heartbeat
Gallstones
Fatigue

Common side effects are more varied and less frequently linked to the gastrointestinal system. While some digestive symptoms, like indigestion, bloating, gas, and heartburn, can occur, these are less likely than the very common side effects mentioned before.

These and other side effects, like dizziness and injection site reactions, are usually manageable and go away after a few days. Others (like hair loss, low blood pressure, and gallstones) can persist, and may require assessment from a healthcare professional, just to be safe.

A sketched list of common side effects of Mounjaro, complete with bullet points and images

Uncommon side effects

The following uncommon side effects affect up to 1 in 100 people:

Gallstones
Changes in taste

Injection site pain
Odd skin sensations

These uncommon side effects are only felt by around 1 in 100 to 1 in 1000 people, so you’re unlikely to experience them yourself. If you do experience any of these side effects, it’s important to speak with your doctor and discuss your best next steps.

In my experience, side effects involving changes in taste or skin sensation tend to be mild and temporary, resolving as the body adjusts to the medication. However, some patients report that it can affect their quality of life, and may decide to lower their dose or stop treatment.

If you’re experiencing side effects, it’s important to bring it up with your doctor so you can both come up with a plan that works best for you.

A sketched list of uncommon side effects of Mounjaro, complete with bullet points and images

At what point do side effects usually start?

Most side effects of Mounjaro are experienced within a few days of taking it for the first time. However, they’re unlikely to last very long, particularly the most common gastrointestinal ones.

If you get mild side effects after taking it for the first time, try not to worry too much. This usually just means the medicine is working. If side effects come on later on in your treatment, consider talking it through with your doctor so they can determine the cause.

How long do Mounjaro side effects last for?

Most side effects only last for a few days while your body gets used to the medicine, but they can persist for a little longer, and some people may only get them on higher doses. Remember, individual responses to treatment vary.

If side effects persist or they become severe, stop taking Mounjaro and speak with a qualified healthcare professional. They may need to adjust your treatment plan. In my own experience, lowering the dose is usually enough to fix the problem, but in some cases, I have had to recommend a different weight loss treatment entirely.

When to contact a doctor

Some side effects are more serious and may require attention from a healthcare professional.

Serious side effects:

Inflamed pancreas (acute pancreatitis): This can cause severe pain in the back and stomach that doesn’t go away, with or without vomiting.
Severe allergic reactions: Symptoms of this include breathing problems, swelling of the face, lips, and throat, difficulty swallowing, and a fast heartbeat.

If you get signs of either of these after taking Mounjaro, it’s important to go see a doctor immediately. While most cases aren’t, it can be life-threatening.

For a full list of safety warnings, read the patient information leaflet.

Managing side effects: a doctor’s expert tips

Based on my experience prescribing Mounjaro, here are my top tips for managing the most common side effects:

For gastrointestinal side effects:

Eat bland foods: Simple foods like crackers, toast, and rice are easy on the stomach and may reduce the severity of gastrointestinal issues.
Eat smaller, more frequent meals: Eating too much at once can put stress on your digestive system. Smaller meals can make it easier on your stomach.
Avoid fatty and spicy foods: These can cause digestive issues and make side effects worse. You don’t have to cut them out completely, just limit your intake.
Eat more fibre: Gradually add more whole grains, fruits, and vegetables to your diet. Be cautious not to overdo it, as too much fibre too quickly can cause bloating and gas.
Stay hydrated: Drink plenty of water to support your digestion and overall health.
Time your injection: Injecting at night might help you sleep through the initial period of peak nausea.

For injection site reactions:

Rotate injection sites: Use different areas of your thigh, upper arm, and stomach weekly to avoid bruising and swelling.
Let the medicine reach room temperature: Sometimes, medicine injected directly from the fridge can cause discomfort. Consider letting it sit for an hour or so before injecting.
Keep the area clean: Use an alcohol swab to clean the injection site before use.

The bottom line

Mounjaro can be a highly effective weight loss treatment, and knowing what to expect when it comes to side effects and how to manage them is key to a successful treatment journey.

While the majority of side effects are mild and temporary, if you experience anything severe or persistent, contact a healthcare professional immediately. At the end of the day, your health and safety should be the top priority, and you shouldn’t suffer in silence if you’re experiencing side effects.

The best way to ensure safety during treatment is to trust your care to a licensed healthcare provider like euroClinix. Not only do we offer professional consultations to ensure safe prescribing, we also offer additional support every step of the way, including helping you deal with potential side effects.