Quick answer: GLP-1 fatigue is a recognized but less common side effect. Fatigue or weakness was reported by 11% of adults on Wegovy 2.4 mg versus 5% on placebo, and by 5% to 7% of adults on Zepbound versus 3% on placebo.[1][2] The most likely causes are a sharp drop in calories, not drinking enough, stomach side effects and, for some people with diabetes, low blood sugar.
Below we cover the label data for Ozempic, Wegovy, Mounjaro and Zepbound, what is probably behind the tiredness, and what you and your clinician can do about it. For more on how these drugs work, start at our GLP-1 basics hub and the semaglutide and tirzepatide profiles.
Do GLP-1 drugs make you tired? What the labels say
Each FDA label lists side effects that happened more often on the drug than on placebo. Fatigue appears in the weight-loss labels, where doses are higher.
| Drug | Fatigue on drug | Fatigue on placebo | Notes |
|---|---|---|---|
| Wegovy 2.4 mg | 11% | 5% | Includes fatigue and asthenia (weakness) |
| Wegovy 7.2 mg | 11% | 5% | 2.4 mg arm in the same trials: 9% |
| Zepbound 5 / 10 / 15 mg | 5% / 6% / 7% | 3% | Includes asthenia, lethargy and malaise |
| Ozempic | Listed | Not stated | Reported in more than 0.4% of people |
| Mounjaro | Not in main table | — | Main table lists side effects at 5% or more |
Sources: Wegovy, Zepbound, Ozempic and Mounjaro labels.[1][2][3][4]
In short: most people on these drugs do not report fatigue, but it is several percentage points more common than on placebo at weight-loss doses.
Why semaglutide and tirzepatide can make you tired
The labels do not explain why fatigue happens, and no trial has pinned down a single cause. These are the most plausible contributors, based on how the drugs work and on their known side effects.
Eating much less
These drugs reduce appetite strongly. In the STEP 1 trial, people on semaglutide 2.4 mg lost an average of 14.9% of body weight over 68 weeks, and in SURMOUNT-1, people on tirzepatide 15 mg lost 20.9% over 72 weeks.[5][6] Losing weight that quickly requires a large calorie deficit, and some people simply are not eating enough to feel energetic, especially in the early weeks or after a dose increase.
Dehydration
Nausea, vomiting and diarrhea can drain fluids, and a reduced appetite can mean drinking less too. The Wegovy label warns that dehydration from stomach side effects has led to acute kidney injury in some people.[1] Mild dehydration commonly causes tiredness and dizziness.
Stomach side effects
Feeling queasy, bloated or constipated can disrupt sleep and make you feel run down. See our guide to GLP-1 nausea for how long it usually lasts.
Low blood sugar in people with diabetes
On its own a GLP-1 rarely causes hypoglycemia, but the risk rises when combined with insulin or a sulfonylurea. In a Wegovy trial in people with type 2 diabetes, blood sugar below 54 mg/dL was reported in 6% on the drug versus 2% on placebo. The labels say insulin or sulfonylurea doses may need to be lowered.[1][2] Shakiness, sweating, confusion and sudden tiredness can be signs.
Other causes worth checking
Rapid weight loss can unmask or coincide with other problems such as anemia, thyroid issues, poor sleep or low mood. Fatigue is not always the drug, so it is worth a check-up if it persists.
How long does GLP-1 fatigue last?
There is no published average. Because the likely causes (low intake, nausea, fluid loss) are strongest during dose escalation, many people find tiredness eases once they settle on a maintenance dose. The labels note that stomach side effects mostly occur during escalation and decrease over time.[2][4]
How to manage fatigue on a GLP-1
These steps target the likely causes. They are general suggestions; your clinician can tailor them.
- Eat enough protein and regular small meals. Even with a small appetite, aim for something nourishing at each meal rather than skipping meals.
- Drink fluids through the day. Do not wait to feel thirsty, especially if you have diarrhea or vomiting.
- Keep moving gently. Light activity and resistance exercise can help energy and protect muscle during weight loss.
- Check your blood sugar if you have diabetes and take insulin or a sulfonylurea, and ask whether those doses should change.
- Watch alcohol, which can worsen dehydration and low blood sugar. See GLP-1s and alcohol.
- Talk about the dose. Wegovy’s label allows a clinician to delay a dose increase or use a lower maintenance dose if side effects are hard to tolerate.[1]
Fatigue on diabetes doses (Ozempic and Mounjaro)
People taking Ozempic or Mounjaro for type 2 diabetes generally use lower doses than the weight-loss versions, and fatigue is less prominent in those labels: Ozempic lists it among less common reactions, and it is not in Mounjaro’s main table of side effects seen in 5% or more of people.[3][4] In people with diabetes, tiredness can also come from blood sugar that is running too high or too low, so home glucose readings are a useful clue.
Questions to ask your clinician
- Should my next dose increase be delayed until I feel better?
- Am I eating enough protein and calories for my activity level?
- Should my insulin or sulfonylurea dose change?
- Is it worth checking blood counts, iron, vitamin B12 or thyroid function?
- Could another medicine, poor sleep or low mood be playing a part?
Fatigue and other common side effects
Fatigue often shows up alongside GLP-1 headaches, nausea and GLP-1 hair loss, all of which tend to track with fast weight loss. If you are not seeing results despite side effects, our guide on not losing weight on a GLP-1 covers what to discuss with your prescriber.
This article is general information, not medical advice. Your clinician sets your dose and can help work out what is behind your tiredness.
