GLP-1 Help

Side effects · Using · Question 6 of 35

Why do I feel so tired?

Tiredness is a real, listed side effect. Why it happens has not been studied directly, so this page separates the measured part (how often) from the reasoned part (why).

By Dr. Chiranjeevi Peetla · Updated November 2026 · 4 min read · 3 sources, each linked

How common

Fatigue (which in the labels includes weakness, called asthenia) was reported by 11% on Wegovy 2.4 mg against 5% on placebo, and by 11% on the 7.2 mg dose.[1] On Zepbound it was 5%, 6% and 7% at 5, 10 and 15 mg, against 3%; the Zepbound figure also counts lethargy and malaise.[2] So roughly one extra person in 15 to 25 feels tired because of the drug.

Possible reasons, labelled honestly

No trial has measured the cause of fatigue on these drugs. The following are reasonable contributors, each tied to something that is measured:

  • Eating much less. Energy intake fell by roughly a quarter to a third in feeding studies.[3]
  • Fluid loss. Vomiting and diarrhea plus drinking less can dehydrate, which the labels flag.[1][2]
  • Low blood pressure. Hypotension-related events were 1.3% versus 0.4% on Wegovy, more often in people on blood pressure medicines.[1]
  • Low blood sugar, mainly in people with diabetes also taking insulin or a sulfonylurea.[1][2]

Which of these applies to a particular person is something a clinician can check; it is not something a website can tell.

When it may be something else

  • Fainting, or dizziness every time you stand
  • Shakiness, sweating, confusion if you take insulin or a sulfonylurea (possible low blood sugar)
  • Tiredness with very little urine after days of vomiting or diarrhea
  • Low mood that lasts: see the mood page

Heard vs evidence

"Everyone feels exhausted on it."
About 1 in 9 on Wegovy and 1 in 14 to 20 on Zepbound reported fatigue, and part of that would have happened on placebo anyway.[1][2]

The short version

Short on the way. A 35-second captioned version of this page is in production for the Fewer Bites channel. It will be embedded here when it is live.

Questions to bring to your prescriber

Print these or screenshot them. They are conversation starters, not a checklist of things to do.

  • Could my tiredness be low blood pressure, low blood sugar or dehydration, and how would we check?
  • Should any of my other medicines be reviewed now that I am eating less and losing weight?
  • Would blood tests help rule out other causes?

Education, not advice. This page explains what trials, labels and guidelines report. It does not tell anyone to start, change or stop a medicine. Your prescriber knows your history; this page does not.

Sources

Every number on this page traces to one of these. "Primary read" means the full paper or label was read; "abstract only" means only the abstract was available; "secondary" means the figure was taken from a named review.

  1. Novo Nordisk / FDA. Wegovy (semaglutide) injection and tablets, prescribing information, revised 06/2026. label
  2. Eli Lilly / FDA. Zepbound (tirzepatide) prescribing information, revised 08/2026. label
  3. Christensen S et al. Dietary intake by patients taking GLP-1 and dual GIP/GLP-1 receptor agonists: a narrative review. Obesity Pillars 2024. secondary · review

Forums

Dizziness and low blood pressure

Read

Eating

Full after three bites

Read

Using

Headaches

Read

Safety

Mood and depression

Read

All 35 questions