Obesity, type 2 diabetes, and being overweight all share fatigue as a common factor. Treating these conditions should, theoretically, alleviate any symptoms of excessive tiredness. However, one of the treatments used to tackle obesity, Mounjaro (tirzepatide), may be linked to causing further fatigue in a small minority of people. According to a recently published study on Wegovy (a similar drug to Mounjaro),1 7% of participants experienced side effects, some of which felt more tired than usual.1
Monjaro is a weekly subcutaneous injection (administered in the fatty tissue, just under the skin) approved for use both in treating high blood sugar for those with type 2 diabetes, and more recently, to help with weight reduction in those struggling with obesity. While clinical trials on this drug have shown significant promise in its effectiveness, helping people lose around 15-20% of their body weight, tiredness and fatigue are not listed as side effects, despite complaints from users stating otherwise.2
It’s important to understand that Mounjaro, just like Ozempic, Wegovy, and Saxenda, is a medication that’s relatively new to the market for treating weight loss, meaning that clinical trials are still ongoing to give us some more definitive answers regarding its side effects.3
That being said, certain side effects of Mounjaro can inadvertently cause tiredness. For instance, it is well known that these medicines, labelled as GLP-1 receptor agonists, can cause several gastrointestinal disturbances including bloating, nausea, and vomiting, all of which can make it harder for you to fall asleep and get about your day, which in turn contributes to fatigue.1
When Mounjaro first received approval, the Food and Drug Administration (FDA) did not list tiredness as a potential side effect. However, the FDA pointed out that the clinical trials were conducted under very controlled conditions, which might not mirror real-world experiences.4 In everyday use, numerous factors can influence side effects. For instance, trial participants often don't have the underlying conditions that many people do, and they aren't taking other medications that might cause fatigue. Additionally, lifestyle behaviours can vary widely outside of a trial setting. So, while tiredness wasn't observed in the controlled environment of the trials, it could emerge when the medication is used by a broader, more diverse population.
For tiredness to be listed as a common side effect, it must have occurred in at least 5% of the participants. While the clinical trials for Mounjaro involved a relatively large number of participants, the percentage affected by fatigue might have been too small to note. However, when millions of people worldwide are taking Mounjaro, the incidence of tiredness can appear more frequent, making it seem more common than it actually is.
GLP-1 receptor agonists work by mimicking the effects of a natural hormone called glucagon-like peptide 1 which stimulates the body to produce more insulin when their blood sugar rises.4 This is the case for specific GLP-1 receptor agonists like Ozempic and Saxenda. However, Mounjaro has a dual effect, working as both GLP-1 receptor agonist and a glucose-dependent insulinotropic polypeptide (GIP) receptor agonist, which exerts similar effects to GLP-1.5
Because Mounjaro targets multiple pathways, it might bring with it more side effects than the likes of Ozempic and Wegovy. This effect may lead to a lower calorie intake which causes your body to slow down its metabolism and preserve its energy stores, causing you to feel more tired than usual.
GLP-1 receptor agonists took the world by storm when they were first introduced to the market to help people lose weight. TikTok, Instagram and Reddit were flooded with people sharing their experiences. One study carried out in 2023 analysed thousands of comments and videos across social media to try and get a better understanding of the real-world effects of these medicines.6
Out of the thousands of posts or entries reviewed, the authors of the study found that the majority of complaints were related to sleep issues such as insomnia, anxiety, depression, and mental health issues in general. Some people found that their mental health improved, which should be the case when losing weight, however, some found that their mood deteriorated, accentuating a sense of fatigue and tiredness.
Weight loss medicines aren’t designed as lifelong medicines that allow you to eat what you want. They’re there to help boost weight loss in those who have adopted healthier lifestyles. If you’re struggling with fatigue and are taking Mounjaro for weight loss, don’t hesitate to reach out to our health coaches who will be more than happy to help guide you to adopt a healthier lifestyle that will make you feel better and full of energy.
Richards, R., Wren, G. M., Campion, P., & Whitman, M. (2023). A remotely delivered, semaglutide-supported specialist weight management program: Preliminary findings from a retrospective service evaluation. JMIR Formative Research, 7(1), e53619. doi:10.2196/53619
Jastreboff, A. M., Aronne, L. J., Ahmad, N. N., Wharton, S., Connery, L., Alves, B., … Stefanski, A. (2022). Tirzepatide once weekly for the treatment of obesity. The New England Journal of Medicine, 387(3), 205–216. doi:10.1056/nejmoa2206038
McDonald, M., & Farrah, K. (2022). Tirzepatide for Type 2 Diabetes Mellitus. Canadian Agency for Drugs and Technologies in Health.
Latif, W., Lambrinos, K. J., Patel, P., & Rodriguez, R. (2024). Compare and Contrast the Glucagon-Like Peptide-1 Receptor Agonists (GLP1RAs). StatPearls Publishing.
Gettman, L. (2023). New drug: Tirzepatide (mounjaroTM). The Senior Care Pharmacist, 38(2), 50–62. doi:10.4140/tcp.n.2023.50
Arillotta, D., Floresta, G., Guirguis, A., Corkery, J. M., Catalani, V., Martinotti, G., … Schifano, F. (2023). GLP-1 receptor agonists and related mental health issues; Insights from a range of social media platforms using a mixed-methods approach. Brain Sciences, 13(11), 1503. doi:10.3390/brainsci13111503
