Does a GLP-1 Make You Tired? What the FDA Labels Say

Yes — tiredness is a real, documented adverse reaction on some of these drugs, and it is written into their FDA labels. But the number you have probably seen quoted online is very likely one that does not appear in any label at all, or one that has been lifted from the wrong product, or the wrong table inside the right product. This page does something almost nobody publishing on this topic does: it reads the actual prescribing information for all five of the major GLP-1 and GIP/GLP-1 products, side by side, and reports exactly what each one says — including the two that say nothing.

Two framings to set up front. First, "fatigue" on a drug label is not a mechanism, it is a count of how many people in a trial reported feeling tired and told an investigator about it. Second, the number that matters is never the drug column on its own. It is the drug column next to the placebo column, because a substantial share of people report fatigue on placebo too.

The FDA label table, side by side

Read that table for thirty seconds and the picture changes from the one you get on a med-spa blog. Three of the five products tabulate fatigue with a placebo comparator. Two do not tabulate it at all.

Wegovy (semaglutide 2.4 mg) lists it in Table 3 of its label as a composite — footnote b of that table states it "includes fatigue and asthenia" — at 11% on drug versus 5% on placebo across 2,116 treated adults and 1,261 placebo¹. That is the largest labeled drug–placebo gap in the class, and it means roughly one in twenty people gets fatigue attributable to the drug rather than to being in a weight-loss trial.

Zepbound (tirzepatide) lists it in Table 1 as a broader composite — footnote e: "includes asthenia, fatigue, lethargy, malaise" — and reports it by dose: 5% at 5 mg, 6% at 10 mg, and 7% at 15 mg, against 3% on placebo². The dose-response is the interesting part: the gradient across doses is exactly what you would expect if the drug were contributing, rather than the trial setting.

Saxenda (liraglutide 3 mg) is the only one of the five that does not use a composite. Its adult table breaks the two terms out separately: fatigue 7.5% versus 4.6%, and asthenia 2.1% versus 0.8%³. That is a useful accident of drafting, because it shows how much of a composite number is ordinary tiredness versus the more specific complaint of weakness.

Ozempic (semaglutide, for type 2 diabetes) does not tabulate fatigue anywhere. It appears only in a short narrative paragraph headed "Fatigue, Dysgeusia and Dizziness," which says other adverse reactions with a frequency of greater than 0.4% associated with Ozempic include fatigue, dysgeusia and dizziness⁴. There is no percentage, no denominator, and — critically — no placebo comparator. "Greater than 0.4%" is a reporting threshold, not a rate.

Mounjaro (tirzepatide, for type 2 diabetes) does not mention it at all. Not in a table, not in a narrative paragraph, not in the patient information. The words fatigue, asthenia, lethargy and malaise do not appear anywhere in the label⁵.

Three traps in reading these numbers

The reason coverage of this topic is so unreliable is that the labels are easy to misread in three specific ways. If you take nothing else from this page, take these.

Trap 1: tirzepatide's fatigue rate exists only in the obesity label. Zepbound and Mounjaro are the same molecule. They are different applications with different trial programs, and the fatigue data live entirely in the obesity/OSA one²⁵. Carrying the 5–7% figure across to Mounjaro is a common error and it is not defensible: the diabetes trials are a different population on a different dose schedule, and whatever they found, the FDA did not require it in that label. If you are on Mounjaro, the honest answer to "what percentage of people get fatigue" is the label does not say.

Trap 2: Wegovy has two different fatigue numbers, and you must name the table. Fatigue is 11% in Table 3, which pools the 2.4 mg trials against placebo¹. But the same label's Table 4 — a separate, later trial pool comparing placebo, 2.4 mg and 7.2 mg — reports fatigue at 5% on placebo, 9% on 2.4 mg, and 11% on 7.2 mg¹. Same drug, same dose, same label, two different percentages, because they are different trial populations. Neither is wrong. A citation that says "Wegovy fatigue is 11%" without naming the table is not wrong either, but it is not reproducible, and if someone quotes 9% at you they are also reading the label correctly.

Trap 3: with Saxenda, the usual adult-versus-paediatric tell does not fire. Many drug labels contain an adult adverse-reaction table and a separate adolescent one, and writers grab the wrong table constantly. The usual giveaway is a 0% placebo rate, which almost never happens in a large adult trial. Saxenda breaks that heuristic: its adult table (Table 2) and its paediatric table (Table 3) both report non-zero placebo fatigue — 4.6% in adults and 3.2% in the 12-to-under-18 trial³. So you cannot spot the error by looking at the placebo column. You have to check the denominators: N=1,941 placebo and N=3,384 Saxenda is the adult table; N=126 and N=125 is the paediatric one. The figures on this page are the adult rows.

And one corollary worth stating plainly: anyone publishing a specific Ozempic fatigue percentage is not getting it from FDA labeling. They may be quoting a trial publication, a different product's table, or nothing at all — but the number is not in the label, because the label does not contain one.

So does semaglutide make you tired? Does tirzepatide?

On the labeled evidence: semaglutide at the obesity dose, yes, in about 11% of people versus 5% on placebo — a genuine but minority effect¹. Tirzepatide at obesity doses, yes, in 5–7% versus 3%, rising with dose². Liraglutide at the obesity dose, yes, 7.5% versus 4.6%³. For the diabetes formulations of the same two molecules, the labels do not support a number in either direction⁴⁵.

Notice how modest those gaps are. Subtract the placebo column and the drug-attributable excess is roughly 6 percentage points for Wegovy, 2–4 for Zepbound, and 3 for Saxenda. Fatigue is a labeled reaction, not a near-universal one — and the majority of people who feel tired on these drugs would have to be explained by something other than a direct pharmacological effect.

What is actually making you tired

This is where the label stops helping and mechanism starts. The tiredness people describe on a GLP-1 is usually downstream of how well the drug is working rather than a direct action on the brain, and the broad evidence does not show this class worsening mood or cognition at a group level⁶. Four drivers account for most of it.

You are eating far less than you think. Appetite suppression is the point of the drug, and a great many people end up well below their energy needs without registering it, particularly in the first weeks after a dose increase. That is the single most common explanation for new fatigue on a GLP-1, and it usually comes with the additional tell of feeling cold and losing strength in the gym.

You are mildly dehydrated. Nausea, vomiting, diarrhoea and simply not feeling like drinking add up fast. A fluid deficit of only 1–2% of body weight measurably worsens fatigue, mood and attention, generally before you feel thirsty⁷. It is the most fixable item on this list, and we cover the threshold and the correction in dehydration and brain fog.

Your blood sugar is low or unstable. GLP-1s rarely cause outright hypoglycaemia on their own in people without diabetes, but combined with very low intake, skipped meals, or insulin or a sulfonylurea, low glucose is a direct and well-documented cause of tiredness and slowed thinking⁸. If your fatigue comes with shakiness or sweating and lifts after you eat, that is the pattern — and it is a prescriber conversation, especially on combination therapy. The wider picture is in blood sugar and brain fog.

You are not sleeping as well as you assume. Reflux, nocturnal nausea and interrupted sleep are common early on, and short or fragmented sleep independently degrades attention, working memory and processing speed⁹. If the tiredness is worst on waking and improves through the morning, read why you wake up foggy before you blame the injection. Untreated sleep apnoea is its own major contributor here — and one of these drugs is now actually approved to treat it, which we cover in Zepbound for sleep apnea.

When it usually starts, and when to call someone

The labeled fatigue is concentrated early. Saxenda's label is explicit about this: events of asthenia, fatigue, malaise, dysgeusia and dizziness "were mainly reported within the first 12 weeks of treatment" and were often co-reported alongside gastrointestinal events like nausea and vomiting³. That co-reporting is the most informative sentence in any of the five labels, because it points at the same causal chain described above — feeling sick, eating and drinking less, feeling wiped out — rather than at a direct sedating effect.

Practically: expect the first week or two after each dose escalation to be the worst of it, and treat persistent fatigue past that as a signal to check intake, fluids and sleep rather than to push through. Fatigue that is severe, that does not improve between escalations, or that comes with dizziness on standing, a racing heart, or new neurological symptoms is worth a call to your prescriber rather than a supplement. And nothing here is a reason to change your own dose.

The bottom line

Fatigue is labeled for the obesity products and unlabeled for the diabetes ones. Wegovy 2.4 mg: 11% versus 5% in Table 3, 9% versus 5% in Table 4 — name the table¹. Zepbound: 5%, 6%, 7% by dose versus 3%, as a composite that includes asthenia, lethargy and malaise². Saxenda in adults: fatigue 7.5% versus 4.6%, asthenia 2.1% versus 0.8%, with the adult table identifiable by its N of 1,941 and 3,384³. Ozempic: a narrative mention above a 0.4% reporting threshold with no comparator⁴. Mounjaro: nothing⁵. The drug-attributable excess is real but small, and for most people who feel tired on a GLP-1 the answer is under-eating, dehydration, unstable blood sugar or disrupted sleep — all of which are checkable, and none of which require guessing at a percentage that was never published. If what you are noticing is mental haze rather than physical tiredness, that is a different question, and we take it apart in brain fog on Ozempic and other GLP-1s and in what the GLP-1 cognition trials found.