Unsure about the immediate and long-term side effects of Mounjaro? This handy guide gives you a good understanding of the most queried symptoms – from mild reactions to those that might need more attention. Get to know what to look out for so you feel confident and prepared on your weight loss journey.
Mounjaro (tirzepatide) works by activating two hormone receptors - GLP-1 and GIP - that regulate blood sugar, slow stomach emptying, and reduce appetite. Most side effects stem from these mechanisms, particularly the impact on the digestive system. They are most common when starting treatment or increasing the dose, and typically improve as your body adjusts.
Digestive side effects
Reduction in appetite
Mounjaro does suppresses your appetite. It works by stimulating two hormone receptors: glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). GLP-1 helps regulate blood glucose levels by slowing down the emptying of the stomach to keep hunger at bay. GIP enhances the effects of GLP-1 by regulating the energy balance in your brain and fat cells. This is an intended effect of Mounjaro and is a contributing factor to weight loss.
Read our full guide to Mounjaro and appetite suppression
Nausea & Vomiting
Nausea is a common side effect of Mounjaro. In research trials, 1 in 5 Mounjaro users reportedly experienced nausea. tirzepatide (the active drug in Mounjaro) slows down gastric emptying, which can lead to feelings of fullness and discomfort, especially when starting treatment or increasing doses.
Vomiting is a reported side effect of Mounjaro, although it's less common than nausea, with approximately 9% of users reported sickness during treatment. It's typically associated with higher doses or rapid dose escalation and may accompany nausea in some cases. Eating smaller meals throughout the day and avoiding greasy, fried foods can help keep nausea and vomiting at bay.
Read our full guide to Mounjaro nausea and vomiting
Diarrhoea & Constipation
Diarrhoea is another common side effect of Mounjaro, reported by approximately 16% of users during clinical trials. This is due to the impact of tirzepatide on gastrointestinal motility (the movement of food through the digestive tract) and digestion. While not everyone experiences diarrhoea, it can occur, particularly during the initial weeks of treatment as your body adjusts.
Constipation is another side effect of Mounjaro, reported in around 5–10% of patients (depending on dose), although it'sless common than diarrhoea. Constipation can occur because of delayed gastric emptying caused by the medication. Increasing your fibre intake alongside getting enough fluid (2-3 litres per day) helps reduce this symptom.
Read our full guide to Mounjaro constipation and diarrhoea
Sulphur Burps
Excessive burping can be unpleasant but can be common when taking a medication that affects the digestive system. Mounjaro is a glucagon-like peptide-1 (GLP-1) agonist, which means it binds to and activates GLP-1 receptors,mimicking the effects of the natural GLP-1 hormone. This hormone slows down gastric emptying, which causes food and liquid to stay in the stomach longer and can increase the amount of gas created. When food or other substances in your stomach are broken down, the fermentation created bybacteria can produce sulphur-containing gases, leading to burps.
Read our full guide to Mounjaro and sulphur burps
Bloating
Some people experience bloating when starting Mounjaro - a feeling of fullness, tightness, or visible swelling in the abdomen. This happens because slowed gastric emptying causes food and gas to build up in the stomach for longer. Eating smaller portions, avoiding fizzy drinks and gas-producing foods, and staying active can all help reduce symptoms. For most people, bloating settles down as the body adjusts to the medication.
Read our full guide to Mounjaro and bloating
Acid reflux (heartburn)
The Mounjaro injection can cause acid reflux (heartburn) for some people. This can be due to excess stomach acid build-up which occurs because of delayed gastric emptying. Avoiding trigger foods such as spicy dishes, citrus fruits, caffeine and alcohol, and eating smaller, more frequent meals can help alleviate discomfort.
Read our full guide to Mounjaro and heartburn
Stomach pain
Stomach pain or abdominal discomfort is a potential side effect of Mounjaro, as well as indigestion (a feeling of discomfort or fullness in the upper abdomen). Around 7% of users reported stomach pain (dyspepsia) during clinical trials. It may be related to nausea, slowed gastric emptying, or other gastrointestinal effects of the drug.
Most gastrointestinal side effects like nausea, diarrhoea, and reduced appetite, tend to decrease over time as the body adjusts to the medication. If these symptoms persist or get worse, speak to a member of our clinical team who'll help you manage symptoms or adjust your dose.
Energy & Sleep Side Effects
Insomnia
You may have heard about people experiencing insomnia as a result of taking Mounjaro and other weight loss medications. But it's not listed as a common side effect by the manufacturer.
Read our full guide to Mounjaro and insomnia
Tired/Lethargy
Some people feel more tired, lethargic and weak while adjusting to eating less, particularly in the early weeks of weight loss treatment. Tirzepatide, the active ingredient in Mounjaro, works by suppressing your appetite, which may lead to consuming less calories than you're used to. As your body adjusts to a lower calorie intake, you can feel tired. Make sure you're consuming nutrient-dense foods and protein to meet your body's energy needs. As you get used to your new medication, your body may go through an adjustment period, of which tiredness can be a side effect. Make sure you speak to one of our expert clinical team if you're concerned about your energy levels.
Read our full guide to Mounjaro and tiredness
Feeling cold
Some people on Mounjaro report feeling unusually cold, particularly in the hands and feet. This can be related to reduced caloric intake, as the body generates less heat when consuming fewer calories, or to changes in circulation as weight loss progresses. It is generally a temporary effect that improves over time.
Read our full guide to feeling cold on Mounjaro
Pain and other physical side effects
Muscle loss
Experiencing muscle loss when losing weight is normal. To reduce this, make sure you're eating regular meals and snacking on high protein foods. Resistance or strength training also helps to build and maintain your muscle mass during weight loss.
Remember, Mounjaro's side effects vary from person to person with many not experiencing any at all. Whether you want to start your weight loss journey or have questions about the symptoms you're experiencing, our expert clinical team are here to listen and support you, every step of the way.
Read our full guide to preventing muscle loss on Mounjaro
Headaches
Headaches have been anecdotally reported as a side effect of Mounjaro. Changes in food and liquid intake, as a result of taking Mounjaro, may cause dehydration-related headaches. Headaches can also be a symptom of low blood glucose levels. Speak to our expert clinical team if you're experiencing consistent headaches while taking Mounjaro.
Read our full guide to Mounjaro and headaches
Body aches, joint pain, and back pain
Some people on Mounjaro report musculoskeletal symptoms including body aches, joint pain, and back pain. These can occur as the body adapts to rapid weight changes, reduced caloric intake, or changes in physical activity levels during treatment. In most cases these symptoms are mild and temporary.
Read our full guide to Mounjaro and body aches
Dizziness
Dizziness is a known side effect of taking this medication. Mounjaro works by mimicking the hormones GLP-1 and GIP, which stimulate the release of insulin from the pancreas after a meal. This insulin works to regulate your blood glucose levels. It's well-known that not eating and drinking enough can lead to feelings of dizziness. Speak to one of our expert clinical team if you're experiencing frequent dizziness as a result of taking Mounjaro to avoid self-diagnosis.
Hair & skin side effects
Hair loss
Research shows that hair loss can be a possible side effect of taking Mounjaro. A meta-analysis performed on eight studies found that, in one of those studies, approx. 5.2% of participants experienced hair loss due to tirzepatide (the active drug in Mounjaro). However, this may not be directly related to tirzepatide, . Increased hair shedding can be common with significant changes in caloric intake. Eating nutrient-dense foods can help reduce hair loss, particularly protein, healthy fats and the micronutrient biotin also known as vitamin B7.
Read our full guide to Mounjaro and hair loss
Hormonal & systemic side effects
Mental health effects
Some patients report changes to their mood, anxiety levels, or low mood while taking Mounjaro. These effects may be linked to hormonal changes associated with weight loss, shifts in energy levels, or the psychological impact of significant dietary changes.
Read our full guide to Mounjaro and mental health (anxiety and depression)
Sex drive
Changes in sex drive have been reported by some people taking Mounjaro. These effects may be linked to hormonal changes associated with weight loss, shifts in energy levels, or the psychological impact of significant dietary changes. The relationship between GLP-1 medications and libido is an area of ongoing research.
Read our full guide to Mounjaro and sex drive
Bladder health & UTIs
Bladder issues and urinary tract infections (UTIs) are not officially listed as common Mounjaro side effects, but some users have reported changes in urinary frequency or occasional UTIs. These are most likely linked to dehydration caused by gastrointestinal side effects, or to immune changes associated with rapid weight loss, rather than a direct effect of tirzepatide. Staying well hydrated is the most effective preventive measure.
Read our full guide to Mounjaro and bladder health
Serious but rare side effects
Pancreatitis
Pancreatitis is a possible side effect of Mounjaro. However, this risk is generally considered rare. Mounjaro may increase enzyme activity in the pancreas, which could, in very rare cases, lead to inflammation. Also, if you have gallstones, Mounjaro can also slightly increase your risk of developing gallstone-related issues such as gallstone pancreatitis. If you're using Mounjaro and develop signs of pancreatitis, such as severe abdominal pain (especially radiating to the back), nausea, vomiting, or a fever, you must seek medical attention immediately.
Read our full guide to Mounjaro and pancreatitis
Mounjaro & existing health conditions
Mounjaro and hyperthyroidism
Hyperthyroidism is not a contraindication for Mounjaro, but it is a consideration when prescribing. Because both conditions affect metabolic pathways, clinicians assess each patient's thyroid health and current medications before prescribing tirzepatide. People with well-controlled hyperthyroidism may still be eligible for treatment, subject to individual clinical assessment.
Read our full guide to taking Mounjaro with hyperthyroidism
What happens when you stop taking Mounjaro?
When you stop taking Mounjaro, appetite typically returns to pre-treatment levels and the metabolic effects of tirzepatide gradually wear off. Understanding what to expect when discontinuing treatment is important for managing weight long-term and planning next steps with your clinical team.
Read our full guide to stopping Mounjaro
References
https://pubmed.ncbi.nlm.nih.gov/37908750/
https://www.ncbi.nlm.nih.gov/books/NBK585056/#:~:text=Tirzepatide%20is%20a%20dual%20agonist,1%20medications%20such%20as%20semaglutide.
https://pmc.ncbi.nlm.nih.gov/articles/PMC5315033/
https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4709105
https://www.lilly.com/news/media/media-kits/mounjaro
https://bpspubs.onlinelibrary.wiley.com/doi/10.1111/bph.15611
https://pmc.ncbi.nlm.nih.gov/articles/PMC10614464/#sec2
https://pmc.ncbi.nlm.nih.gov/articles/PMC10614464/
