Mounjaro Fatigue: Why It Happens & Simple Steps to Combat It

Last updated: 19 November, 2025

If you are feeling sluggish or tired on Mounjaro, you’re not alone. Many patients report feeling fatigued and low on energy on the treatment.

As it’s still a relatively new medication, we don’t yet know why you might experience Mounjaro fatigue. However, there are several possible explanations for it. And the good news? You can feel more energised by taking a few simple steps.

To help you feel your best during your treatment, this article explores the link between Mounjaro (tirzepatide) and fatigue. And we’ll provide practical tips to combat exhaustion on your weight loss journey, so you can focus on building long-term health gains.

Can Mounjaro Make You Tired?

Yes. Mounjaro can make you tired.

Not everyone will feel tired on Mounjaro, but it’s a common Mounjaro side effect. It affects between one in 10 and one in 100 patients.

Most patients will experience tiredness when they’re starting Mounjaro and it’s usually temporary. You should feel less fatigued as your body adapts to both the treatment and new lifestyle changes.

Why Does Mounjaro Make You Tired?

There are no clinical studies explaining why you might lack energy on Mounjaro injections.

However, Mounjaro works by mimicking two hormones, naturally produced in the body, that help regulate appetite and blood sugar. These hormones are glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1).

By mimicking these hormones, Mounjaro slows down the rate at which food leaves the stomach (known as “delayed gastric emptying”). This means you feel fuller quicker and stay fuller for longer.

So, while we don’t know the exact cause, there are some theories that could explain why you feel tired. Here are some possible explanations.

You’re Eating Less

Mounjaro reduces your appetite and makes you feel full sooner, which is why it’s such an effective weight loss treatment. However, if you eat too little on Mounjaro, this might contribute to fatigue.

“Mounjaro often leads to a significant decrease in food intake, which can lead to consuming fewer nutrients. This can ultimately impact your energy levels,” Laura Perez, Lead Dietitian at Simple Online Pharmacy, explains.

Mounjaro Impacts Your Hormones

Mounjaro injections affect your metabolism by influencing hormones that regulate blood sugar and appetite. These metabolic changes might make you feel tired, especially during the initial adjustment period.

Side Effects Can Cause Fatigue

Potential side effects include diarrhoea, being sick and nausea, which can increase the risk of dehydration and electrolyte imbalances. Both of these can cause tiredness and fatigue.

Mounjaro Might Affect Your Sleep Cycle

Mounjaro works by sending signals to the area of your brain that produces hormones controlling hunger, body temperature and mood.

This area (the hypothalamus) also regulates sleep and wakefulness. So it’s possible the medication could be impacting your sleep-wake cycle.

Your Blood Sugar is Low

Mounjaro doesn’t directly cause low blood sugar. However, there is some association between GLP-1 receptor agonists and low blood sugar.

Low blood sugar is common in patients using GLP-1 pens alongside type 2 diabetes medication. (For example, sulphonylurea and/or insulin medication.)

Malnutrition can also lead to low blood sugar. So you could experience it if you’re undereating on Mounjaro.

Symptoms of low blood sugar may include feeling tired or weak, as well as headaches, dizziness and hunger. You may also feel cold, as your body struggles to regulate body heat. If you think you have low blood sugar, contact your healthcare provider.

How to Combat Mounjaro Fatigue

To combat fatigue, focus on making small adjustments to support your overall wellbeing. 

As you incorporate the following strategies, you’ll likely begin to feel better throughout your weight loss journey.

Eat Enough Nutrient-Dense Food

Eating enough nutrient-dense foods is one of the best ways to combat fatigue on weight loss medications. Avoid skipping meals completely.

“Even if you aren’t able to eat large portions, focus on nutrient-dense foods. This will provide essential vitamins and minerals that help maintain your energy levels,” Laura advises.

“Incorporate a variety of fruits, vegetables, whole grains, lean proteins and healthy fats into your meals. This way you can ensure you’re getting the necessary nutrients to support your body.”

These foods will provide a steady energy source throughout the day. Avoid simple sugars and highly processed foods. They can cause rapid spikes and crashes in energy, which is exactly what we want to avoid.

Remember to aim for steady weight loss of 1-2 lbs per week, rather than rapid weight loss. This will help you sustain your success in the long-term.

Exercise Regularly

Exercise can boost energy levels, improve your mood and promote better sleep. Some studies have also found gentle exercise can help combat fatigue.

Of course, exercise might seem like the last thing you want to do when feeling tired. But some light exercise every day can make you feel more awake and energised.

Pushing yourself too hard can make you even more tired. Listen to your body and avoid overly intense workouts.

Start small, with gentle exercises like walking, yoga or swimming. Gradually increase the intensity and duration of your workouts as your energy levels improve.

Build a Sleep Routine

“Prioritise rest and make sure you’re getting enough sleep. Recovery is vital for maintaining your overall wellness,” Laura says.

A consistent sleep routine can regulate your body’s natural sleep-wake cycle. This cycle is “necessary to replenish and heal the body to ensure that it can function properly”. It will help you recharge and feel energised the next day.

Here are some steps you can take for better sleep:

• Go to sleep and wake up at the same time every day.
• Get seven to nine hours of sleep every night.
• Create a relaxing bedtime routine that includes, for example, reading a book or meditating.
• Avoid bright screens, especially blue screens such as smartphones and laptops.
• Avoid consuming caffeine within four to six hours before bedtime.

Manage Stress Levels

When stress becomes chronic, it can drain your energy and make fatigue worse.

Techniques like meditation, deep breathing exercises, hobbies or gentle exercise can help you manage stress levels.

Stay Hydrated

Common side effects of Mounjaro like nausea, vomiting and diarrhoea can cause dehydration. A symptom of dehydration is tiredness. This happens because your tissues aren’t getting the amount of fluid they need to function.

Hydration on GLP-1s is important for a number of reasons, including the prevention of dehydration-related fatigue. If you have persistent vomiting and/or diarrhoea, let your healthcare provider know.

Key Takeaways

• What Causes Fatigue on Mounjaro? The exact cause is unknown; there are no clinical trials that explain it. Potential reasons may include reduced food intake, hormonal changes, side effects like nausea and dehydration. Sleep cycle disruptions and lower blood sugar levels might also play a role.
• Eat Enough Nutrient-Dense Food: Focus on eating nutrient-dense foods as you lose weight. A balanced diet is essential for maintaining energy levels. Reduced food intake and blood sugar fluctuations can lead to fatigue.
• Exercise Regularly and Manage Stress: Gentle exercise can help boost energy, improve mood and promote better sleep. Chronic stress can drain your energy and worsen fatigue but techniques like meditation can help you manage stress.
• Prioritise Rest: Get enough sleep and maintain a consistent sleep schedule. Go to bed at the same time each night, minimise screen time before bed and avoid caffeine late in the day. This can help regulate your sleep cycle and reduce fatigue.

• Stay Hydrated: Side effects like nausea, vomiting and diarrhoea can cause dehydration, which can worsen fatigue. Make sure you drink plenty of water and stay hydrated throughout the day.
• Get Support: Get advice from your healthcare provider if symptoms persist. Let them know if you suspect you have low blood sugar. If you’re a patient with Simple, call us on 0141 774 5023.

References

Mendoza, F., Parsiani, R., 2019. Impact of tirzepatide in a patient with type 1 diabetes and obesity: A case report. Journals of the American Pharmacists Association. 63(6), pp.1821-1825. [online]. Available from: https://pubmed.ncbi.nlm.nih.gov/37604405/.

Whyte, M. (2023). Mounjaro has been authorised for weight loss in the UK – here’s how it compares to Wegovy. [online] The Conversation. Available at: https://theconversation.com/mounjaro-has-been-authorised-for-weight-loss-in-the-uk-heres-how-it-compares-to-wegovy-217413.

National Institute of Neurological Disorders and Stroke (2024). Brain basics: Understanding sleep. [online] National Institute of Neurological Disorders and Stroke. Available at: https://www.ninds.nih.gov/health-information/public-education/brain-basics/brain-basics-understanding-sleep.

Reddy, S., Sharma, S. and Reddy, V. (2023). Physiology, Circadian Rhythm. [online] NIH.gov. Available at: https://www.ncbi.nlm.nih.gov/books/NBK519507/.

Puetz, TW., Flowers, SS., O’Connor, PJ., 2008. A randomized controlled trial of the effect of aerobic exercise training on feelings of energy and fatigue in sedentary young adults with persistent fatigue. Psychotherapy and Psychosomatics. 77(3), pp.167-74. [online]. Available at: https://pubmed.ncbi.nlm.nih.gov/18277063/.

Kranz, R. (2024). Symptoms of dehydration: What they are and what to do if you experience them. [online] Harvard Health. Available at: https://www.health.harvard.edu/staying-healthy/symptoms-of-dehydration-what-they-are-and-what-to-do-if-you-experience-them.

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