Mounjaro specifically
Table 1 of the Mounjaro® label covers two placebo-controlled trials in adults with type 2 diabetes and lists only reactions reported by at least 5% of people on the medicine and more often than on placebo. Fatigue is not on it, and the Mounjaro® Medication Guide does not list tiredness among the most common side effects [1][2].
The label does mention fatigue once more: in a cardiovascular outcomes trial of 6,647 adults with type 2 diabetes and established heart disease, fatigue was reported by 10% of people on Mounjaro®. The label lists it as one of a few exceptions to an otherwise similar safety picture, without a comparison figure next to it [1].
The European Mounjaro® information, which covers diabetes and weight management under one name, classes fatigue as very common. Its footnote explains that fatigue was very common in the cardiovascular trial and common in the weight, sleep apnoea, heart failure and type 2 diabetes trials [10].
Trial rates against placebo
US labels for medicines approved for weight reduction do list fatigue in their tables. Ranges cover dose groups. The Ozempic® label says only that fatigue was reported in more than 0.4% of people, with no placebo comparison [6].
| Label and trial pool | Placebo | Medicine |
|---|---|---|
| Zepbound®: Studies 1 and 2, adults with obesity or overweight [3] | 3% | 5% to 7% |
| Wegovy® 2.4 mg: 3 trials, adults with obesity or overweight [5] | 5% | 11% |
| Wegovy® 7.2 mg: Studies 8 and 9 [5] | 5% | 11% (9% on 2.4 mg) |
| Saxenda®: weight trials in adults [7] | 4.6% | 7.5% |
| Foundayo™ (daily tablet): Trials 1 and 2 [8] | 4% | 6% to 9% |
European and Canadian product information
The European Medicines Agency uses frequency classes rather than single percentages. It lists fatigue as “very common” for Wegovy® and Mounjaro® and as “common”, at least 1 person in 100, for Ozempic® [9][10][11]. There is no European Zepbound® document, because tirzepatide is sold in the EU only as Mounjaro®.
The Canadian Zepbound® monograph reports fatigue in 4.6% to 6.8% of people across doses against 3.1% on placebo in SURMOUNT-1 and -2, counting asthenia, lethargy and malaise under the same heading [12].
What the word covers
The labels group related terms together. In the Zepbound® table, fatigue includes asthenia (weakness), fatigue, lethargy and malaise. In the Wegovy® tables it includes fatigue and asthenia. The Saxenda® label lists asthenia separately, at 2.1% against 0.8% on placebo [3][5][7].
Section 6.1 of each label adds that rates from different trials cannot be directly compared, so these numbers describe each label’s trials rather than rank the medicines.
When it tends to appear
Among the US labels, only Saxenda® gives timing. It says asthenia, fatigue, malaise, taste changes and dizziness came up mostly in the first 12 weeks on the medicine, frequently alongside stomach reactions such as nausea, vomiting and diarrhea [7]. The European Wegovy® table points the same way, marking fatigue as mainly seen during dose escalation [9].
The other labels do not say when fatigue started or how long it lasted, so the timing in your own notes is information the labels cannot give you.
Warnings that can feel similar
- Low blood sugar: the Medication Guides list weakness, confusion or drowsiness, dizziness, shakiness and sweating among its possible signs. The risk is higher with insulin or a sulfonylurea [2][5]. In a Zepbound® trial in adults with type 2 diabetes, low blood sugar was reported by 10.3% of those also taking a sulfonylurea, against 2.1% of those who were not [12].
- Dehydration: the guides point out that fluid lost through diarrhea, nausea or vomiting can dry you out and, in turn, affect the kidneys [2][4]. The NIH lists feeling tired, dizzy or lightheaded among the signs of dehydration, along with thirst, dark urine and passing less urine [15].
- Low blood pressure: in the Zepbound® trials it occurred in 1.6% on the medicine versus 0.1% on placebo; in the Wegovy® trials, related reactions occurred in 1.3% versus 0.4%, and fainting in 0.8% versus 0.2%. The labels say some cases were linked to stomach reactions and fluid loss [3][5].
- These are separate entries in the labels. Sorting out which one, if any, explains your tiredness is your clinician’s job.
Why it may happen
What the labels support: fatigue was more common on these medicines than on placebo, it clustered in the early weeks and around dose increases in the Saxenda® and European Wegovy® information, and it often came with stomach reactions [7][9]. The labels also link stomach reactions to fluid loss, and diabetes medicines such as insulin and sulfonylureas to low blood sugar [2][5].
What is proposed but not measured: these medicines reduce how much people eat. In one early trial described in the European Wegovy® information, people on semaglutide ate 35% less at a free-choice meal than on placebo [9]. Eating noticeably less could plausibly leave some people feeling flat, but no label names reduced intake as a cause of fatigue.
General medical background: MedlinePlus notes that many conditions and medicines cause tiredness on their own, including diabetes itself, so fatigue on a GLP-1 medicine is not automatically a side effect of it [13].
What else could it be
MedlinePlus lists many causes of fatigue: anaemia and iron deficiency, an underactive or overactive thyroid, sleep problems such as insomnia or obstructive sleep apnoea, depression or grief, persistent pain, alcohol, and illnesses such as infections, heart failure, and kidney or liver disease [13].
It also names medicines that can cause drowsiness or fatigue, including antihistamines, blood pressure medicines, sleeping pills, steroids, diuretics, sedatives and some antidepressants [13]. If you started or changed any of these around the same time, mention it.
What may help
The Medication Guides do not give fatigue-specific advice, and Novo Nordisk’s Wegovy® page simply asks you to tell your healthcare professional how you are feeling [14]. MedlinePlus offers general self-care for fatigue; it is not written for GLP-1 medicines.
- Get enough sleep, keep a balanced diet and drink water through the day [13].
- Exercise regularly, find ways to relax and keep a manageable schedule [13].
- Avoid alcohol and nicotine. Caffeine and other stimulants are not effective treatments for fatigue and can make it worse when stopped [13].
- Ask your provider before taking supplements, and do not stop or change any prescribed medicine on your own [13].
What to write down
Tiredness is vague until it is dated. Note the day and time of day you felt it, how many days after your injection that was, how long it lasted and how strong it felt. Add your sleep, roughly how much you ate and drank, and whether nausea, vomiting or diarrhea came on the same days. If you check your blood sugar, note readings taken when you felt unwell.
After a few weeks you can see whether tiredness clusters in the first days after a dose, follows days of eating little, or is fading as treatment goes on. That pattern is the most useful thing to bring to your clinician.
Mounjaro® and Zepbound® are registered trademarks and Foundayo™ is a trademark of Eli Lilly and Company. Wegovy®, Ozempic® and Saxenda® are registered trademarks of Novo Nordisk A/S. PepLabo is not affiliated with or endorsed by Eli Lilly and Company or Novo Nordisk.
When to get help
| Sign | Who to contact | How fast | Source |
|---|---|---|---|
| Thoughts of harming yourself or of suicide | Your healthcare provider right away | Emergency | MedlinePlus [13] |
| Tiredness with confusion, dizziness, blurred vision, or little or no urine | Your healthcare provider right away | Today | MedlinePlus [13] |
| Weakness, shakiness, sweating, confusion or drowsiness, especially if you use insulin or a sulfonylurea | Follow the low blood sugar plan from your provider and contact them | Today | Medication Guides [2][5] |
| Nausea, vomiting or diarrhea that keeps going, with signs of dehydration | Your healthcare provider, without delay | Today | Medication Guides [2][4] |
| Unexplained tiredness with fever, weight loss you did not expect or regular sweats | Book an appointment with your provider | At your next appointment | MedlinePlus [13] |
| Tiredness that bothers you or does not go away | Your prescriber | At your next appointment | Medication Guides [2][4] |
