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Side effects

Tiredness on a GLP-1 medicine

Feeling wiped out in the first weeks is common, and people are often surprised by it. The labels record it, and the reasons are mostly unglamorous: less food, less fluid, and a gut that is busy adjusting. It usually eases. When it does not, it is worth a conversation rather than a shrug.

By the Cafeity teamUpdated 4 min read

The short answer

Tiredness (fatigue) is a listed side effect of GLP-1 medicines: 11% of people on semaglutide 2.4 mg reported it against 5% on placebo, up to 7% on tirzepatide against 3%, 7.5% on liraglutide 3 mg against 4.6%, and up to 9% on orforglipron against 4%.1234 The liraglutide label notes that tiredness, weakness and dizziness were mainly reported in the first 12 weeks, often alongside nausea, vomiting or diarrhoea.3 Eating too little, dehydration and poor sleep all contribute. Persistent or severe tiredness, fainting, or signs of low blood sugar need a clinician.

Bar chart of tiredness (fatigue) in the weight-management trials: Semaglutide 2.4 mg 11% versus 5% on placebo; Tirzepatide 7% versus 3% on placebo; Liraglutide 3 mg 7.5% versus 4.6% on placebo; Orforglipron 9% versus 4% on placebo.
Share of trial participants who reported fatigue (including asthenia and similar terms), from each label. Not a head-to-head comparison.

How common it is

Tiredness (fatigue) in placebo-controlled trials, from the current US prescribing information for each medicine. Rates from different medicines' trials are not directly comparable.
Medicine (trial population)PlaceboMedicine
Semaglutide 2.4 mg weekly injection (adults with obesity or overweight)5%11%
Semaglutide 7.2 mg weekly injection (adults with obesity)5%9% (2.4 mg), 11% (7.2 mg)
Tirzepatide weekly injection (adults with obesity or overweight)3%5% (5 mg), 6% (10 mg), 7% (15 mg)
Liraglutide 3 mg daily injection (adults with overweight or obesity)4.6%7.5%
Orforglipron daily tablet (adults with obesity or overweight)4%6% (5.5 mg), 7% (9 mg), 9% (17.2 mg)
Dulaglutide weekly injection (adults with type 2 diabetes)2.6%4.2% (0.75 mg), 5.6% (1.5 mg)

The labels group several related terms together — fatigue, asthenia (weakness), lethargy and malaise — so the numbers describe a general feeling of tiredness rather than one precise symptom.2

Why it happens

No label pins tiredness on a single mechanism, but the context points to a few contributors:

  • Eating much less. The labels say these medicines reduce calorie intake by affecting appetite.1 A sudden drop in food, particularly in protein and carbohydrate, is tiring.
  • Gastrointestinal side effects. The liraglutide label notes tiredness was often reported alongside nausea, vomiting and diarrhoea.3 A day of nausea is a tiring day.
  • Fluid. A smaller appetite often means drinking less, and mild dehydration feels like fatigue.
  • Low blood sugar, for people taking insulin or a sulfonylurea — tiredness, weakness and dizziness are among its signs in the patient information.2

When it tends to ease

The liraglutide label reports that tiredness, weakness and dizziness were mostly seen in the first 12 weeks.3 That fits the broader pattern in which side effects cluster during dose escalation and ease afterwards. Tiredness that starts or worsens months in, or that is getting worse rather than better, is worth raising — it has plenty of causes that have nothing to do with the medicine.

What tends to help

The 2025 joint advisory's general priorities for people on these medicines are also the practical answer to most tiredness: adequate protein, nutrient-dense food, regular meals rather than long gaps, fluids, and strength training.5 The advisory also flags that very low intakes raise the risk of micronutrient shortfalls, and suggests clinicians consider vitamin D, calcium and B12 — a reasonable thing to ask about if tiredness persists.5

Sleep matters too: see sleep on a GLP-1.

When to contact your prescriber

Keeping a record of it

Log energy with a severity and a time, on the same timeline as your doses, meals and fluids. After a few weeks the record shows whether it follows dose increases, particular foods or the days after an injection — and the Visit Summary puts that on one page for your prescriber.

Cafeity dose screen: an estimated medication-level curve labelled "Estimate based on published half-life. Not a measurement", the last dose, the injection site (stomach, lower left), a countdown to the next scheduled dose and a side-effect check-in.
A side-effect check-in under every dose.
Cafeity "Your week, understood" screen: Ora explains that everything is calculated from your own log, offers questions such as "When are my symptoms worst?", and shows the week's protein, energy, water, weight trend, symptom days and a note that protein was 80 g under target.
Ask when your symptoms are worst.

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Common questions

Why am I so tired on a GLP-1?
Common contributors are eating much less, gastrointestinal side effects and drinking less. The liraglutide label reports tiredness mainly in the first 12 weeks, often alongside gut symptoms.3
Does GLP-1 tiredness go away?
For most people it eases as the dose settles. If it does not, or gets worse, tell your prescriber — tiredness has many causes worth checking.
Is it tiredness the day after the injection?
Some people notice a dose-day pattern, which may follow nausea and lower eating on those days. Logging energy daily for a few weeks will show whether you have one.

Sources

  1. Semaglutide injection and tablets for weight management — US prescribing information DailyMed, US National Library of Medicine, version published 30 June 2026
  2. Tirzepatide injection for weight management and obstructive sleep apnoea — US prescribing information DailyMed, US National Library of Medicine, version published 2 September 2026
  3. Liraglutide 3 mg injection for weight management — US prescribing information DailyMed, US National Library of Medicine, version published 15 June 2026
  4. Orforglipron tablets for weight management — US prescribing information DailyMed, US National Library of Medicine, version published 13 August 2026
  5. Nutritional priorities to support GLP-1 therapy for obesity: a joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society Mozaffarian D et al. 2025 (published in four journals)

Written by the Cafeity team from the sources listed here. Figures from prescribing information are quoted as the label states them; trial results are averages from those trials, not predictions for any one person. This page has not yet been reviewed by a clinician — see the editorial policy for how pages are researched and corrected.