Before you start any treatment, it’s helpful to be aware of potential side effects you might experience. Side effects won’t be the same for every person who uses the Mounjaro, so there are no guarantees how the injections will affect you. But they can start at any dosage, and might increase as you switch to a higher strength pen.
Mounjaro is an injectable pen treatment for diabetes and weight loss. It contains tirzepatide, an antidiabetic medication that targets two receptors, GLP-1 and GIP — hormones known as incretins. Incretins play a vital part in controlling appetite and regulating blood sugar levels.
Another way Mounjaro works is by slowing down gastric emptying. This means food empties from your stomach at a reduced rate, which can help you feel fuller for longer after you’ve eaten.
You inject Mounjaro into your stomach, upper arm or upper leg once a week. The pens come in six doses. You usually start on the lowest dose, then move up to a different strength pen every four weeks until you reach the highest strength, maintenance dose.
Here, we’ll take a look at the common and rare side effects Mounjaro can cause, as well as answering some frequently asked questions about what to expect while using this treatment.
Common Mounjaro side effects are thought to affect more than one in ten people.
Low blood sugar (hyperglycaemia) is mentioned as a very common, common and uncommon side effect when tirzepatide is used to manage type 2 diabetes, and taken with different diabetes medications such as insulin, sulfonylurea and metformin. You’re less likely to experience this effect when using Mounjaro for weight loss, without these other medications.
Tirzepatide has been assessed for its safety and effectiveness during trials across eight countries. The SURPASS-5 trials involved 475 adults with type 2 diabetes who used tirzepatide over 40 weeks. The most common side effects experienced were nausea, diarrhoea and vomiting.
Any side effects you experience while using Mounjaro should ease off as your body adjusts to the medication. Whenever you change to a higher dose pen, you might find side effects start again. This is completely normal, and they should still be manageable, and reduce, as you get used to your new dose.
If any side effects you get feel intolerable, you can speak to a clinician about alternative weight loss treatments that might be a better fit for you.
In placebo-controlled clinical trials for diabetes, gallbladder disease was reported by less than 1% of patients who were treated with tirzepatide. While you’re unlikely to experience uncommon side effects while using Mounjaro, it’s still important to be aware of them.
If you notice unusual side effects developing, such as those listed above, stop using the injections and contact a clinician. Gallstones can sometimes cause severe pain if they block bile ducts; if you get any severe symptoms that come on suddenly, go to your nearest hospital and get urgent medical attention.
Serious side effects caused by Mounjaro are divided into two two categories:
Uncommon (may affect up to 1 in 100 people)
An inflamed pancreas usually causes severe, lasting stomach pain. It’s often accompanied by nausea or vomiting, and a high temperature.
Rare (may affect up to 1 in 1000 people)
Serious allergic reactions can cause breathing difficulties, swollen lips, and difficulty swallowing. They can also lead to anaphylaxis, which can be life threatening.
If you develop any of these serious side effects, go immediately to your nearest hospital’s emergency department.
Mounjaro can cause excessive gas and burping for some people. Burping is listed as a common side effect in the patient information leaflet (PIL), along with other gastrointestinal effects including acid reflux and indigestion.
Although they’re not specifically listed in the PIL, the injections have been known to cause ‘sulphur burps’ for some people. These are burps with a distinct, unpleasant smell.
If you get sulphur burps, there are some things to try that might ease them. Make a note of any food and drinks that make your burping worse and try to avoid them. Some foods, like legumes and dairy products, are rich in sulphur, which could potentially make you more prone to this side effect.
Avoiding fizzy drinks might also help. To relieve burping, try eating and drinking more slowly, as chewing for longer can help break the food down better and help digestion. Antacids, which neutralise stomach acid, might also help.
Hair loss ‘observed in patients treated for weight loss’ is listed as a common Mounjaro side effect. In one study that looked at patients using tirzepatide for 52 weeks, 4% of users experienced hair loss.
Losing weight, especially if it’s a significant amount in a short space of time, is known to contribute to hair loss. Like stress, certain illnesses, and iron deficiency, these changes are usually temporary.
More research is needed to find out exactly why weight loss can sometimes impact hair growth, but it’s thought that nutritional deficiencies and hormonal imbalances might play a part.
As with other side effects, not everyone who uses Mounjaro will experience hair loss. While hair loss is listed as a possible side effect, tirzepatide has also been shown to promote hair growth.
Reflux is another common Mounjaro side effect, and can develop for one in ten people using the pens. Like nausea and a decreased appetite, it’s a gastrointestinal effect that can be unpleasant and uncomfortable. Because tirzepatide slows down digestion, excess acid can build up and lead to reflux, which can cause heartburn and create an unpleasant taste in your mouth.
Any acid reflux you experience while using the pens should settle as your body adjusts to the medication, but like other side effects, might return when you change doses.
If you get reflux often, there are some things that can help. Eating small, frequent meals rather than large ones might help to reduce stomach acid. Wearing clothes that fit loosely around your waist might also help.
As with other side effects, like burping, identifying foods that make your reflux worse will mean you know what to avoid. Alcohol is known to make acid reflux and GORD (Gastro-oesophageal reflux disease) symptoms worse, so it might be helpful to reduce your intake while using Mounjaro.
Overeating while using Mounjaro might make any side effects you get worse.
Because Mounjaro slows down digestion, it can help you feel fuller. This means urges to snack or overeat during meals should be reduced. As well as counteracting your weight loss efforts, overeating can induce Mounjaro’s gastrointestinal side effects, such as bloating or cramping. If you feel the urge to overeat while using the pens, it could be that you need to switch doses.
Fatigue is included in the list of common Mounjaro side effects, so there is a chance you might feel tired when you start using the pens.
But tiredness might occur during a weight loss plan for various reasons. You might feel like eating fewer calories impacts your energy levels, as you adjust to consuming less than you normally would.
What you eat can also affect your energy. The injections will make you want to eat less, but you’ll still need to maintain a varied diet to meet all your nutrition needs. A lack of protein, for example, could lead to muscle loss, which in turn could cause tiredness.
Excessive thirst isn’t listed as a side effect in Mounjaro’s patient information leaflet. If you often feel thirsty while using the pens, it could be a sign that you’re dehydrated. Because Mounjaro makes you feel fuller, eating less might mean your fluid intake is also affected.
Staying hydrated while using Mounjaro can help improve your digestion, and should mean you feel less thirsty throughout the day. If the medication reduces urges to eat and drink, it might be helpful to set yourself reminders to drink throughout the day. You could also set a daily drink target to help you stay properly hydrated.
You might also feel thirsty if Mounjaro has caused diarrhoea or vomiting, as your body will want to replenish any fluids you’ve lost. It might be helpful in this case to use a rehydration sachet, to also replace lost electrolytes and body salts.
Mounjaro will affect each person differently. If you get side effects while using it, they should ease off as you adjust to the medication. This might be in a matter of days, but for some people things might take a bit longer to settle.
Any side effects you do experience might start up again when you change pens, which you’ll usually do every four weeks. If you feel like the side effects you experience are persistent, it might be that the increased dose doesn’t suit you. In this case, you might be able to remain on a dose you’re comfortable with that causes the least amount of side effects, if you’re happy with how that dose is working for you.
You shouldn’t get Mounjaro side effects long-term. The gastrointestinal effects Mounjaro can cause, such as diarrhoea and vomiting, could put your health at risk if these effects don’t settle.
Both of these side effects can cause dehydration, which can impact kidney function if it isn’t treated and becomes severe. But if any side effects persist throughout your treatment and remain uncomfortable, you should speak to a clinician about them.
Mounjaro is only available as a weight loss treatment if your BMI is over 30, or if it’s over 27 and you have a weight-related condition, like pre-diabetes. If you have any long-term health conditions that regular Mounjaro use might impact, a clinician will consider any long-term risks before it’s prescribed to you.
You can speak to a clinician about any side effects concerns you have before you start using Mounjaro. Although its patient information leaflet lists common, less common and rare side effects, how you react to Mounjaro might differ from how you’d expect. If any side effects you experience put you off using Mounjaro, you can talk to a clinician about them. They’ll advise you about ways you can manage side effects, or recommend alternative weight loss treatment if they think they’ll be better suited to you.
Eating smaller meals more often and trying to practise mindful eating, rather than eating large main meals, might help to reduce symptoms. The pens should help to reduce your appetite, but it’s also important to stay hydrated while using them. Drinking water often can help digestion, which can improve acid reflux.
If your reflux symptoms are worse in the evening, you might find raising the head of your bed (so it’s above your waist) helps. It can also help you get restful sleep by preventing symptoms from disturbing you during the night.
“Effect of Subcutaneous Tirzepatide vs Placebo Added to Titrated Insulin Glargine on Glycemic Control in Patients with Type 2 Diabetes: The SURPASS-5 Randomized Clinical Trial.” JAMA, vol. 327, no. 6, 8 Feb. 2022, pp. 534–545.
“What Proportion of Patients Developed Gallbladder Disease during the Mounjaro® (Tirzepatide) Clinical Trial Program for Type 2 Diabetes (T2D)?” Lilly.com.
“Antacids.” PubMed, StatPearls Publishing.
Public assessment report. Tirzepatide.
Hair Loss.
“Treatment of Insulin Resistance with Tirzepatide Leading to Improvement of Hair Loss.” JAAD Case Reports, vol. 50.
Conditions: Heartburn and acid reflux.
“Is Alcohol Consumption Associated with Gastroesophageal Reflux Disease?” Journal of Zhejiang University.
Last updated on Aug 06, 2024.
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