GLP-1 fatigue

Each label counts tiredness a little differently, so each count is printed with its label.

• Wegovy (Prescribing Information, revised February 2026): fatigue, counting fatigue and asthenia together, in 11 in 100 people on the 2.4 mg injection against 5 in 100 on placebo. Dizziness was 8 against 4, and headache 14 against 10.
• Zepbound (Prescribing Information, revised January 2026): fatigue, counting asthenia, fatigue, lethargy, and malaise together, in 5, 6, and 7 in 100 people on the 5, 10, and 15 mg doses, against 3 on placebo. Dizziness was 4 to 5 against 2.
• Ozempic (Prescribing Information, revised May 2026): fatigue appears among other adverse reactions with a frequency above 0.4 in 100, with no table row of its own.
• Mounjaro (Prescribing Information, revised January 2026): the diabetes trial table lists reactions reported in at least 5 in 100 people, and fatigue is not among them. Decreased appetite is, at 5 to 11 in 100 against 1 on placebo.

The patient-facing pages say the same thing in plain words. Novo Nordisk says feeling tired is a common side effect seen with Wegovy and to let your healthcare professional know how you are feeling (Novo Nordisk, Wegovy side effects page, May 2026). The NHS lists feeling tired among the common side effects of both semaglutide and tirzepatide (NHS Medicines, last reviewed 15 May 2026).

None of the labels says why fatigue happens or when in treatment it tends to show up. The rest of this page is the causes the other sources name, with their owners.

Both labels say the drug decreases calorie intake, with the effect likely mediated by appetite (Wegovy Prescribing Information, February 2026; Zepbound Prescribing Information, January 2026). The advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association, and The Obesity Society says significant reductions in caloric intake can produce insufficient intake of essential vitamins and minerals, especially under 1,200 kcal a day for women and under 1,800 kcal a day for men (Mozaffarian et al., Obesity Pillars, June 2025).

The same advisory lists fatigue beyond expected levels among the signs of frank nutrient deficiency, alongside excessive hair loss, skin flakiness or itching, muscle weakness, poor wound healing, and unusual bruising (ACLM/ASN/OMA/TOS, June 2025). It says dietary supplements can be proactively considered for at-risk nutrients such as vitamin D, calcium, and B12, a decision for your clinician (ACLM/ASN/OMA/TOS, June 2025).

Every Medication Guide says diarrhea, nausea, and vomiting may cause a loss of fluids, which may cause kidney problems, and that it is important to drink fluids to help reduce your chance of dehydration (Zepbound Medication Guide, January 2026; Wegovy Medication Guide, February 2026; Ozempic Medication Guide, January 2025; Mounjaro Medication Guide, January 2026).

MedlinePlus lists being nauseated as a reason people don't drink enough. It names thirst, a dry or sticky mouth, not urinating much, darker yellow urine, headache, and muscle cramps as signs of mild to moderate dehydration, and dizziness or lightheadedness, a rapid heartbeat, irritability or confusion, and listlessness among the signs of severe dehydration (MedlinePlus, Dehydration, reviewed July 1, 2025). Its prevention advice is to drink plenty of fluids every day, and for anyone with vomiting or diarrhea, to drink plenty of fluids without waiting for signs of dehydration (MedlinePlus, July 1, 2025).

Low blood sugar is a risk the labels tie to other diabetes medicines. Your risk may be higher if you use Zepbound or Ozempic with medicines that can cause low blood sugar, such as insulin or a sulfonylurea, and the listed signs include confusion or drowsiness, weakness, dizziness, shakiness, and hunger (Zepbound Medication Guide, January 2026; Ozempic Medication Guide, January 2025). On Wegovy, low blood sugar in people with type 2 diabetes can be both a serious and common side effect, and the guide says to check your blood sugar before you start and while you take it (Wegovy Medication Guide, February 2026). NIDDK lists tiredness among the mild-to-moderate symptoms of low blood glucose, and names insulin, sulfonylureas, and meglitinides as the medicines that raise the risk (NIDDK, Low Blood Glucose, last reviewed July 2021).

Low blood pressure is on the Zepbound label. It occurred in 1.6 in 100 people on Zepbound against 0.1 on placebo, more often in people also taking blood pressure medicine (2.2 in 100) than in those who weren't (1.2 in 100), and it also occurred in association with stomach side effects and dehydration (Zepbound Prescribing Information, January 2026).

MedlinePlus lists fatigue, lack of energy, or lightheadedness when standing up or with exertion among the symptoms of vitamin B12 deficiency anemia (MedlinePlus, Vitamin B12 Deficiency Anemia, reviewed January 29, 2026). Its list of causes includes long-term use of the medicine metformin, and surgery that removes parts of the stomach or small intestine, such as some weight-loss surgeries (MedlinePlus, January 29, 2026). The advisory names B12 among the nutrients to consider on GLP-1 therapy (ACLM/ASN/OMA/TOS, June 2025).

NHLBI lists weakness, tiredness, shortness of breath, headache, and dizziness among the symptoms of anemia in general (NHLBI, Anemia Symptoms, last updated March 24, 2022). The NHS says someone tired without a clear cause may need tests, such as blood tests to check for anaemia, diabetes, or hyperthyroidism (NHS, Tiredness and Fatigue, 2 June 2023).

The NHS names not getting enough sleep and an unhealthy lifestyle, such as an unhealthy diet and not much exercise, among the common causes of tiredness (NHS, Tiredness and Fatigue, 2 June 2023). Its self-help list is to have a healthy diet and exercise regularly, to stick to the same sleep times and aim for 6 to 9 hours of sleep, to avoid food, caffeine, or exercise in the couple of hours before sleep, to keep screens out of the hour before sleep, and to avoid smoking and too much alcohol (NHS, 2 June 2023).

One trial measured how people felt physically. In STEP 1, people on semaglutide had a greater increase in participant-reported physical functioning than people on placebo (Wilding et al., NEJM 2021).

Sleep apnea is on the Zepbound label, which is indicated to treat moderate to severe obstructive sleep apnea in adults with obesity (Zepbound Prescribing Information, January 2026). The Zepbound guide also asks you to pay attention to any changes in your mood, behaviors, feelings, or thoughts (Zepbound Medication Guide, January 2026).

The NHS says it's best not to drink alcohol on semaglutide or tirzepatide, because it can increase side effects like feeling or being sick (NHS Medicines, 15 May 2026), and it lists drinking too much alcohol among the things to avoid when you're tired (NHS, Tiredness and Fatigue, 2 June 2023). The advisory says alcohol should be minimized on GLP-1 therapy (ACLM/ASN/OMA/TOS, June 2025).

I ask how your energy is each day and keep your answers next to what you ate, how much you drank, how you slept, and your shot days, so a pattern is on the record. When the week shows tired days lining up with low-food or low-fluid days, I read that back to you, and you can hand the same record to your prescriber.

I never diagnose the tiredness, never tell you it's normal, never suggest a supplement, and never change or skip a dose of your medication. When what you describe matches the lines above, a few weeks of tiredness with no clear reason, signs of low blood sugar, fluids you can't keep down, or a change in mood, I say so and tell you to call.

No clinician reviewed this page. It restates the FDA labels, the ACLM, ASN, OMA and TOS advisory, MedlinePlus, NHLBI, NIDDK, the NHS, and the manufacturer's page linked below, and those are the documents to trust over anything here.