7 common Mounjaro side effects and how to navigate them

Are you looking for ways to support your weight loss journey? Often, lifestyle and diet changes alone aren't enough to make your weight loss goals a reality.

In some cases, a talk with your doctor will lead you to explore weight loss medications, such as Mounjaro. Containing the active ingredient tirzepatide, Mounjaro is an injectable medication that belongs to a drug class known as glucose-dependent insulinotropic polypeptide (GIP) receptor and glucagon-like peptide-1 (GLP-1) receptor agonists.

While first formulated to support blood sugar levels in adults living with type 2 diabetes, Mounjaro has shown to be incredibly successful for weight loss, too.

If you're considering using Mounjaro for weight loss, it's important to understand the common side effects of this drug and how to navigate them. Plus, there are rare but serious side effects you need to be aware of, particularly if you have a personal or family history of certain health conditions.

How does Mounjaro work for weight loss?

If you haven't heard of Mounjaro before, it's no surprise as the drug was only recently approved by the US FDA (Food and Drug Administration) [1].

But, you might be more familiar with similar medications, like Wegovy (this contains the active ingredient semaglutide, which is also found in diabetes treatment Ozempic), which have also shown promising signs for weight loss.

What's unique about Mounjaro is that it acts as a dual agonist, activating 2 receptors at once. By activating both the GIP and GLP-1 receptors, Mounjaro effectively stimulates the hormones (such as incretins) that are responsible for managing blood sugar levels and reducing appetite levels.

This medication mimics the hormones naturally present in the body, typically produced by the intestine. Their role is to slow down digestion to help you feel fuller for longer, making it easier to consume smaller portions and manage hunger levels.

With your appetite lower than usual, resetting your eating habits is much easier and weight loss is more attainable, too.

According to clinical trials, GLP-1/GIP treatment is the most effective treatment for weight loss that is available right now. One study¹ of over 2,500 patients from July 2022 found an average of up to 20.9% body weight loss in patients on GLP-1/GIP after 72 weeks. In the same study, up to 90.9% of patients were able to achieve at least 5% weight loss, up to 83.5% were able to achieve at least 10% weight loss and 56.7% were able to achieve at least 20% weight loss in 72 weeks of treatment.

What's most promising is that these trials indicate that Mounjaro can help patients improve their blood sugar levels and rapidly lose weight without putting them at a high risk of hypoglycemia [1].

A more recent meta-analysis in 2023 of more than 10 studies indicates that tirzepatide (the active ingredient in Mounjaro) shows significant weight loss results for patients navigating type 2 diabetes and/or obesity [3].

What are the common side effects of Mounjaro?

Like most drugs, Mounjaro comes with a number of side effects, ranging from mild symptoms like digestive discomfort to more serious side effects (such as severe abdominal pain and an increased risk of gallbladder problems).

Before considering this mediation, make sure to speak with your prescriber or trusted healthcare professional to ensure you've chatted through your family history and assessed whether a Mounjaro prescription is right for you.

Nausea

Nausea is reported as one of the most common side effects of Mounjaro. In fact, studies have shown up to 18% of people will encounter nausea while taking this medication [4].

Like other prescription drugs containing GLP-1 receptors, the higher your dose, the more likely you are to experience side effects, like nausea.

Diarrhoea

Similarly, diarrhoea is a very common side effect of Mounjaro, with clinical trials indicating that 1 in 10 patients will encounter it [4].

Why? It comes back to how Mounjaro works to support significant weight loss and to stabilise blood sugar levels. By slowing down your digestive system, food remains in your stomach for a longer period of time than usual.

While this will have the positive result of reducing your appetite (and therefore the quantity of food you consume to support weight loss), it also can trigger digestive discomfort, from diarrhoea to nausea and beyond.

Decreased appetite

By now, you know that decreased appetite is one of the key side effects of Mounjaro. Like other medications delivered as an injection in a single dose pen, Mounjaro can lead to a significant decline in hunger levels.

This offers benefits if you're looking to manage blood sugar levels and makes it easier to reach your weight loss goals sooner.

Vomiting

While a less common side effect, some patients (5-9%) have reported vomiting while taking Mounjaro [4]. Typically, you'll encounter this side effect alongside nausea and it will be most pronounced in your first few weeks of taking this medication.

Over time, your body will begin to adapt to the medication and any nausea or vomiting should subside. If this doesn't happen or you encounter severe stomach pain, make sure to speak with your prescriber ASAP.

Constipation

Another digestive problem you might notice while taking Mounjaro is constipation. You're not alone: around 7% of people reported this side effect during clinical trials [4].

If you're having less than 3 bowel movements per week, you could be experiencing constipation.

Indigestion

If you're noticing an upset stomach or indigestion while taking Mounjaro, you're encountering one of the most common side effects. This digestive concern usually crops up in patients on a 5mg or 10mg dosage and is usually intensified by eating certain foods (such as greasy meals, spicy dishes, or even drinking alcohol) [5].

Abdominal pain

Another common side effect of this medication is abdominal pain, with up to 5% of patients reporting it while taking Mounjaro [4].

While it should subside on its own, severe stomach pain shouldn't be ignored as it can be a symptom of rare but serious side effects (such as pancreatitis, which is the inflammation of the pancreas).

Again, speak with your doctor ASAP if you notice severe digestive problems or severe pain while taking this medication.

More serious side effects

While much less common, there are a number of rare but serious side effects to be aware of, including:

• Pancreatitis
• Gallbladder problems
• Hypoglycemia (low blood sugar, often linked with blurred vision, dizziness, confusion and slurred speech)
• Severe digestive problems
• Severe allergic reaction

How to mitigate Mounjaro side effects

Mounjaro side effects are typically easy to navigate and treat. With the right action plan, you can combat any of the discomfort you're facing while taking this medication.

If you're encountering nausea or vomiting, try switching to smaller meals, opting for bland foods (like rice, crackers or bread), steering clear of fatty foods, ditching alcohol, and boosting your hydration with clear liquids and plenty of water.

If you're navigating diarrhoea, make sure to stay hydrated with water and electrolyte drinks to keep your body fuelled with the right vitamins and minerals.

If you're navigating constipation, try increasing your fibre intake (opting for fruits, vegetables, and grains), moving your body, and boosting your water intake.

If you're navigating indigestion, lower your intake of caffeine and alcohol, ditch fatty foods, and eat slowly to ensure you're chewing food completely. You might also need to reduce how much food you're consuming to soothe your upset stomach.

How long do Mounjaro side effects last?

There isn't one set answer to this question, but many side effects subside within a few days or weeks, particularly the milder ones that occur as your body gets used to the medication. More severe (yet rarer) side effects can last longer, though. If you're unsure whether the side effects you're experiencing are out of the ordinary, be sure to speak to your doctor.

What you should know before taking Mounjaro

Before taking Mounjaro, make sure to chat with your GP to ensure this medication is right for you.

If you miss a dose, it's important to take your missed dose as soon as possible. If it's been more than 4 days since your dose was due, skip it and continue with your usual dose moving forward.

While less common, some people might experience an allergic reaction while taking Mounjaro (characterised by symptoms like skin rash, itchiness, and flushing). If you notice more severe symptoms (such as swelling under your skin and swelling of your tongue, mouth or throat), you could be having a medical emergency, so seek treatment at a hospital ASAP.

Potential drug interactions

If you're prescribed Mounjaro to manage type 2 diabetes, you might also be prescribed medications to manage your blood sugar levels. These can include drugs such as metformin, insulin, and glimepiride.

It's important to note that taking Mounjaro alongside diabetes medication (such as insulin) can increase your risk of low blood sugar. Your doctor will monitor your blood sugar levels frequently and might need to adjust your dosage to ensure you don't encounter low blood sugar levels.

Does Mounjaro make birth control less effective?

According to a 2024 study, tirzepatide can impact the way the contraceptive pill is absorbed in the body, potentially reducing its effectiveness and leading to unplanned pregnancies [8].

In fact, Mounjaro comes with a warning on the label recommending that those on the pill switch to a non-oral birth control method.

It's also worth mentioning that losing weight can regulate your menstrual cycle and improve your fertility, so your chances of conceiving can increase simply because the medication is doing what it is supposed to do.

But going back to the potential interaction between Mounjaro and the pill — some doctors advise patients to take the latter at least one hour after their injection, and others suggest patients start using condoms weeks before they start weight loss treatment in order to prevent pregnancy.

We recommend you speak with your doctor about this so you can get personalised advice.

With Juniper's Weight Reset Programme, our prescribers are there every step of the way to answer all your questions and make sure you get the most out of your medication while avoiding side effects and drug interactions.

Can Mounjaro cause low blood sugar?

In short, no. When taken alone, studies of Mounjaro haven't shown low blood sugar to be a side effect of this medication.

However, if you are taking Mounjaro alongside other type 2 diabetes medications, you can encounter low blood sugar levels. Make sure to discuss any medications you're currently taking with your prescriber before taking Mounjaro.

Can Mounjaro cause body aches?

No, body aches aren't a common side effect of Mounjaro. However, stomach and abdominal pain are common while taking this medication. If this pain increases dramatically in severity, be sure to chat with your doctor to understand what might be the cause.

Does Mounjaro cause heartburn?

You may experience acid reflux as a result of taking Mounjaro but it should be mild and temporary.

Mounjaro and thyroid cancer: Is there a link?

Interestingly, Mounjaro comes with a boxed warning about the risk of thyroid cancer [7]. This is known as the most serious warning that the FDA can provide, meaning there is the potential that Mounjaro can lead to an increased risk of developing thyroid cancer.

However, this is based on studies of animals that saw an increased risk of thyroid tumours in animals that received this drug [6]. It's unclear whether this risk is also present in humans.

At this stage, it's advised that those with a family history of medullary thyroid carcinoma (MTC) or endocrine neoplasia syndrome type 2 (MEN 2) should avoid taking Mounjaro [7].

Can you take Mounjaro if you're pregnant or breastfeeding?

No, Mounjaro is not advised for anyone pregnant or breastfeeding. Currently, it's unknown whether this medication can cause harm to unborn babies or infants [7].

How to properly take Mounjaro

Mounjaro is delivered as a weekly injection, and it's important to follow your doctor's instructions when it comes to your dosage. Over time, your doctor will slowly increase your dosage as your body adjusts to the medication.

Make sure to inject this medication under your skin using your single-use prefilled pen. Avoid administering your next dose into the same injection site as last time, ensuring you rotate between your abdomen, thigh, and upper arm.

Starting a weight loss journey

Are you looking for a sustainable way to lose weight and keep it off for good? Juniper's Weight Reset Programme combines weight loss medication with personalised health coaching and lifestyle changes.

Mounjaro is a medication option offered in our Weight Reset Programme and it works to suppress appetite and improve metabolic function. As part of our programme, our UK-registered clinicians and dietitians are here to tailor a plan that works for you (including lifestyle coaching, 1:1 health tracking, and access to a private community to celebrate your wins every step of the way).

Find out more and check your eligibility online in minutes.

Mounjaro side effect FAQs

How long do Mounjaro side effects last?

There isn't one set answer to this question, but many side effects subside within a few days or weeks, particularly the milder ones that occur as your body gets used to the medication. More severe (yet rarer) side effects can last longer, though. If you're unsure whether the side effects you're experiencing are out of the ordinary, be sure to speak to your doctor.

Who should not take Mounjaro?

Mounjaro shouldn't be taken by people who have a personal or family history of pancreatitis or medullary thyroid carcinoma, have type 1 diabetes or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2), are allergic to any of the ingredients in Mounjaro, are pregnant, breastfeeding or actively trying to conceive, or take an insulin secretagogue or are on insulin therapy.

What does Mounjaro do to your body?

Mounjaro activates the hormones GLP-1 and GIP to promote weight loss by decreasing your appetite and impacting the pathways that lead to fat loss.