If you are taking Mounjaro, and you are feeling a little more tired than normal, you may be wondering if your tiredness is down to your weight loss medication. It might not be the most talked-about side effect of Mounjaro, but it is something that is reported, both anecdotally and even as an adverse event in the official product information (1). Fortunately, there are things that you can do to limit the impact it has on your day-to-day.
How common is tiredness when taking Mounjaro?
The European Medicines Agency’s official product information leaflet for Mounjaro (tirzepatide) lists fatigue as a common side effect of taking Mounjaro (1). This means that it is known to occur in between 1% and 10% of the people who take it (1).
Why does Mounjaro make you feel tired?
Understanding why Mounjaro may make you feel more tired than normal is very helpful for learning which steps to take to try and reduce the effect that it has. Here are some of the primary reasons why taking Mounjaro could cause fatigue.
Eating less can reduce your energy levels
Eating less can affect your energy levels because your body needs enough calories and nutrients as fuel - for movement, to maintain your blood glucose levels and support essential functions like breathing and movement.
A significant reduction in your food intake may leave you low on elements like carbohydrates, protein, iron and other crucial nutrition. Meanwhile, your body will adapt by using stored energy (which is stored as fat) and reduce your energy expenditure. This can make you feel tired, weak or less able to concentrate, particularly if your weight loss is rapid or your diet is not nutritionally balanced (2).
Side effects can contribute to fatigue
Like all medicines, Mounjaro can cause some side effects, although not everyone gets them. Digestive side effects such as nausea, vomiting and diarrhoea are listed in the Patient Information Leaflet (PIL) as very common (3). This means that they may affect more than 1 in 10 people. The PIL also states that patients may experience fluid loss and dehydration due to vomiting and/or diarrhoea (3). This is because the mechanism of both actions leads to fluids being ejected from your body, often more frequently than you can consume them. But how is this linked to tiredness?
The NHS dehydration guidance clearly states feeling tired as a symptom of dehydration. This is because dehydration reduces the amount of fluid in your body, and this can affect blood volume and the ability of oxygenated blood to circulate around your body (4).
Mild dehydration rarely causes any significant issues but it is still important to know the signs and symptoms. In adults, these include:
Feeling excessively thirsty
Headache
Feeling lightheaded
Dark yellow, strong-smelling urine
Feeling dizzy
Tiredness
A dry mouth, lips and tongue
Sunken eyes
If you are extremely tired and it is accompanied by dizziness, reduced urine output or dark-coloured urine, it is important to seek urgent medical help by calling 111. (4)
Changes in your blood sugar levels can affect your energy levels
Mounjaro is also licensed as a treatment for type 2 diabetes. This is because it works by activating the receptors of two key hormones involved in lowering blood sugar levels (5). Blood glucose is the main source of fuel for many of your body cells. By improving high or fluctuating blood glucose, Mounjaro might help to reduce tiredness that occurred previously due to poor glucose control. However, it does not act as a general energy booster, and fatigue can still occur, particularly if you develop hypoglycaemia.
Hypoglycaemia refers to blood glucose levels that drop below the health range. This is typically under 70 mg/dl (4 mmol/L). It is classed as a medical emergency and needs urgent treatment to stop it getting worse (6).
The risk of hypoglycaemia is increased when Mounjaro is used alongside insulin or some other types of diabetes medications (7).
Signs of hypoglycaemia to be aware of include:
Shakiness or trembling
Sweating/chills
Dizziness/light-headedness
Confusion or difficulty concentrating
Rapid heartbeat
Extreme hunger
If you suspect you may have hypoglycaemia, get immediate medical help by calling 111 or visiting your local Accident and Emergency department (6).
You may just need time to adjust to your medication
Your body needs time to adjust to taking any medication, and Mounjaro is no exception. Clinical studies suggest that gastrointestinal side effects like nausea, vomiting and diarrhoea are most likely to occur while the dose is being increased and often become less frequent over time (8). However, side effects do not improve for everyone, and any new or persistent ones should always be discussed with your prescribing clinician.
How to stop feeling tired on Mounjaro
If you are affected by Mounjaro fatigue, there are steps that you can take that could help you manage or even overcome some of your tiredness.
Eat regular, nutritious meals
Your appetite may be reduced, but eating the right things could help you to reduce Mounjaro-based tiredness. Focus on fibre, protein and complex carbs, healthy fats, fruits and vegetables that provide nutrient-dense meals.
NHS guidance specifically recommends eating meals or healthy snacks every three to four hours to help sustain energy levels throughout the day (9). Complex carbohydrates are best for providing slow-release energy, while other nutrition may help provide a steadier supply of energy to help keep fatigue at bay for longer (10).
Eating regularly may also help to keep any nausea or sickness - that you may be experiencing as a side effect - at bay.
Drink enough fluid
As we know, dehydration can cause tiredness and so drinking enough fluid is very important, with water obviously being the best choice. Drinking enough water can also help to support your long-term weight loss goals, particularly when it replaces higher calorie drinks. Not a fan of plain water? There are low-calorie flavoured waters or squashes that you can add to it to make it more palatable (11).
Get enough sleep
Poor sleep disrupts hormones and metabolism, which can make it harder to lose body fat and maintain a healthy weight. Being tired can also cause cravings for fast energy-release foods, which are typically less healthy (12).
Although everyone needs a different amount of sleep to feel like they function well, current evidence supports a general recommendation for getting seven or more hours sleep per night on a regular basis for optimal health (13).
Stay active
Although it can be hard to motivate yourself to be active when you’re feeling tired, movement actually helps to combat fatigue by boosting your body’s energy production, improving blood flow and releasing specific hormones (9).
When to speak to a doctor about tiredness on Mounjaro
There are some instances, where you should speak to your prescriber or GP about tiredness while taking Mounjaro. This includes:
If tiredness is severe/persistent no matter what steps you take to try and improve it
If your tiredness is accompanied by signs of dehydration
If your tiredness is accompanied by symptoms of low blood sugar
If you are also experiencing severe abdominal pain, persistent vomiting, jaundice or other severe symptoms
Frequently Asked Questions about Mounjaro and Tiredness
How long does tiredness from Mounjaro last?
There is no set time period for how long tiredness from Mounjaro may last. However, if you are actively taking steps to try and improve it, such as those listed above, and you aren’t seeing any difference, we would recommend that you make an appointment with your prescriber or GP for advice.
Does Mounjaro make you feel tired straight away?
It depends on your personal experience as people do not always experience side effects in the same way.
Should I stop taking Mounjaro if I’m tired all the time?
We recommend that you don’t just stop taking Mounjaro without speaking to your prescribing clinician. It may be that your dose needs to be adjusted to balance side effects with the effectiveness of your medicine, or your tiredness may be unrelated. Get in touch with your clinical team to get support.
References
ANNEX I SUMMARY OF PRODUCT CHARACTERISTICS [Internet]. [cited 2026 Sept 13]. Available from: https://www.ema.europa.eu/en/documents/product-information/mounjaro-epar-product-information_en.pdf
NHS. Understanding Calories [Internet]. nhs.uk. 2023 [cited 2026 Sept 13]. Available from: https://www.nhs.uk/live-well/healthy-weight/managing-your-weight/understanding-calories/
Eli Lilly Nederland BV. Mounjaro 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg and 15 mg KwikPen solution for injection in pre-filled pen: package leaflet: information for the patient [Internet]. Leatherhead: electronic Medicines Compendium; 2026 Aug [cited 2026 Sep 13]. Available from: https://www.medicines.org.uk/emc/files/pil.15481.pdf
NHS. Dehydration [Internet]. NHS. 2022 [cited 2026 Sept 13]. Available from: https://www.nhs.uk/conditions/dehydration/
What is Mounjaro® for Adults with Type 2 Diabetes | Mounjaro® (tirzepatide) [Internet]. mounjaro.lilly.com. [cited 2026 Sept 13]. Available from: https://mounjaro.lilly.com/what-is-mounjaro
National Health Service. Low Blood Sugar (hypoglycaemia) [Internet]. NHS. 2023 [cited 2026 Sept 13]. Available from: https://www.nhs.uk/conditions/low-blood-sugar-hypoglycaemia/
Mews K, Momchilovich D. Management of Hypoglycemia Using Continuous Glucose Monitoring During Tirzepatide Initiation or Uptitration When Used in Addition to Other Glucose-Lowering Agents [Internet]. Vol. 38, Diabetes spectrum : a publication of the American Diabetes Association. United States; 2025 [cited 2026 Sept 13]. p. 525–8. Available from: https://pubmed.ncbi.nlm.nih.gov/41257224/
Karrar HR, Nouh MI, Nouh YI, Nouh MI, Khan Alhindi AS, Hemeq YH, et al. Tirzepatide-Induced Gastrointestinal Manifestations: A Systematic Review and Meta-Analysis. Cureus [Internet]. 2023 Sept 27 [cited 2026 Sept 13];. Available from: https://assets.cureus.com/uploads/review_article/pdf/170540/20231030-23491-cmsp7h.pdf
NHS . Self-help Tips to Fight Tiredness - Sleep and Tiredness [Internet]. NHS. 2019 [cited 2026 Sept 13]. Available from: https://www.nhs.uk/live-well/sleep-and-tiredness/self-help-tips-to-fight-fatigue/
Arshad MT, Maqsood S, Altalhi R, Shamlan G, Mohamed Ahmed IA, Ikram A, et al. Role of Dietary Carbohydrates in Cognitive Function: A Review. Food Science & Nutrition. 2025 July;13(7). [cited 2026 Sept 13]. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC12209867/
NHS. Water, Drinks and Your Health [Internet]. nhs.uk. 2023 [cited 2026 Sept 13]. Available from: https://www.nhs.uk/live-well/eat-well/food-guidelines-and-food-labels/water-drinks-nutrition/
Papatriantafyllou E, Efthymiou D, Zoumbaneas E, Popescu CA, Vassilopoulou E. Sleep Deprivation: Effects on Weight Loss and Weight Loss Maintenance. Nutrients [Internet]. 2022 Apr 8 [cited 2026 Sept 13];14(8):1549. Available from: https://www.mdpi.com/2072-6643/14/8/1549/htm
Watson NF, Badr MS. Recommended amount of sleep for a healthy adult: A joint consensus statement of the American academy of sleep medicine and sleep research society. Sleep [Internet]. 2015 June 1 [cited 2026 Sept 13];38(6):843–4. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC4434546/