Zepbound Side Effects: Muscle Pain

Myalgia appears nowhere in the Zepbound prescribing information. Lean mass loss does have numbers. These are two different questions and they have two different answers.

Short answer: muscle pain is not a Zepbound side effect, but lean mass loss is real and they are different things

Muscle pain is not a listed adverse reaction of Zepbound. The words myalgia, muscle pain and musculoskeletal do not appear anywhere in the current US prescribing information, including in the table of reactions reported in at least 2% of treated patients. What is documented is different: in the DXA substudy of SURMOUNT-1, lean mass fell 10.9% over 72 weeks on tirzepatide. That sounds alarming until you read the placebo column, where roughly the same share of lost weight came from lean tissue. So if your muscles ache, the drug is not on the list of causes. If you are worried your muscles are shrinking, that is a separate question with real numbers, and both are below.

A glass of water, a pair of light hand weights on a folded towel and a phone lying face down on a sunlit wooden kitchen counter

Two different worries arrive at this search box wearing the same words. One is a symptom: something aches. The other is a body composition question: am I losing muscle. Pages on this topic generally blur the two, answer neither properly, and cite nothing you can check. The sections below keep them apart, because the evidence for each is completely different, and so is what you would do about it.

Every adverse reaction that did make the Zepbound table

The prescribing information lists reactions that occurred in at least 2% of treated patients and more often than on placebo. This is the complete list, with the column most articles leave out.

Table 1 of the ZEPBOUND US prescribing information, pooled Studies 1 and 2. Percentages of patients.
Adverse reaction Placebo (N=958) 5 mg (N=630) 10 mg (N=948) 15 mg (N=941)
Nausea8252928
Diarrhea8192123
Vomiting281113
Constipation5171411
Abdominal pain59910
Dyspepsia49910
Injection site reactions2688
Fatigue3567
Hypersensitivity reactions3555
Eructation1455
Hair loss1545
Gastroesophageal reflux disease2445
Flatulence2334
Abdominal distension2334
Dizziness2454
Hypotension0112

Sixteen rows. Thirteen of them are the gut, the skin at the injection site, or circulation. Not one is a muscle. There is no row to quote when a page tells you that some percentage of trial patients had muscle pain, because the row does not exist.

What an absent row means, and what it does not

It means myalgia was not reported often enough, or not more often than on placebo, to clear the reporting threshold in trials with thousands of participants. It does not mean nobody aches on Zepbound. Look at the placebo column on fatigue: 3% of people on a saline injection reported it. Ordinary symptoms occur in trials whether or not a drug causes them, which is exactly why a reaction has to beat placebo to earn a line. Muscle pain never did.

The muscle question that does have numbers

Losing muscle and having sore muscles are not the same event, and only one of them has been measured directly. A substudy of SURMOUNT-1 scanned 160 of the 2,539 participants with DXA at baseline and at week 72. Of those, 124 were on tirzepatide and 36 on placebo.

Change from baseline to week 72 in the SURMOUNT-1 DXA substudy, n=160. All comparisons p<0.001.
Measure Tirzepatide (pooled doses) Placebo
Body weight-21.3%-5.3%
Fat mass-33.9%-8.2%
Lean mass-10.9%-2.6%
Share of lost weight that was fatabout 75%about 75%
Share of lost weight that was leanabout 25%about 25%

The last two rows are the finding that changes the question. The split between fat and lean tissue was the same on placebo as on the drug, and it held across subgroups by sex, age and how much weight people lost. Tirzepatide did not change the composition of the loss. It changed how much loss there was. Whatever is taking lean tissue is weight loss itself, not something the molecule does to muscle.

That reframes the worry rather than dismissing it. Twenty-five percent of a large amount is still a large amount, and a 2026 systematic review in Annals of Internal Medicine covering 35 trials found the median share of weight loss coming from muscle-related measures was 28.3%, above the 25% benchmark in about two thirds of incretin studies. The same review recorded something worth knowing before you read anyone's confident conclusion: not one of the 35 studies reported an objective measure of physical function. Nobody has published whether people could lift, climb or stand up any less well afterwards.

So what is making you ache?

Work down this in order rather than starting at the drug, which is last for a reason.

Candidate What points to it Documented where
Dehydration from gut symptoms Aching follows days with vomiting or diarrhea, plus dark urine, light-headedness or a dry mouth Label section 5.3 ties volume depletion after gastrointestinal reactions to kidney injury, so fluid loss on this drug is a documented pathway
New or increased exercise Soreness is in the muscles you worked, starts a day or two after, and eases over a week Not a drug effect. The label indication itself is alongside increased physical activity
Eating much less overall Aching tracks with appetite collapse, and protein intake has quietly fallen with everything else The mechanism behind the lean mass numbers above. A question for your clinician or a dietitian
Fatigue being read as body ache It is diffuse, all over, worse late in the day, with no specific sore muscle Fatigue is on the label at 5% to 7% against 3% on placebo, the only row in Table 1 that is plausibly in this neighbourhood
Something unrelated Everything else: a virus, a new statin, poor sleep, a cold snap, an old injury The default. Muscle pain is common in adults regardless of what they are injecting

A test that separates the drug from the week

You cannot tell cause from a single bad Tuesday. You can tell a lot from four doses, because Zepbound is weekly and almost nothing else in your life is.

  1. For four consecutive weeks, note the day and time of each dose.
  2. Each day, rate the aching 0 to 10, and note where it is: a specific muscle, or everywhere.
  3. Note the days you trained, the days you were short on fluids, and roughly whether you ate normally.
  4. At the end, line the scores up against days since the last dose.

A drug effect looks like a repeating shape: worse on the same days after each injection, across four cycles. Training soreness tracks your sessions, not your doses. Dehydration clusters behind the bad gut days. Something unrelated looks like noise, which is itself an answer. This is the difference between telling your prescriber that your muscles hurt and showing them that the aching peaks two days after every dose, which is a far more useful sentence.

Keep the four weeks in one place

Jabby logs each dose with the date and site, and symptoms against the dose they followed, so the pattern shows up as a pattern rather than a feeling.

Download Jabby, free on the App Store

When this is not a tracking exercise

Stop the diary and contact your prescriber or seek urgent care for severe muscle pain with dark or cola-coloured urine, muscle weakness rather than soreness, pain with fever, severe pain that came on suddenly, or persistent severe abdominal pain, which the label flags separately as a possible sign of pancreatitis. Those are not four week questions. Zepbound is also contraindicated for some people and carries a boxed warning about thyroid C-cell tumours, so anything new and serious belongs with your clinician, not a search engine.

Frequently asked questions

Is muscle pain a known side effect of Zepbound?

No. Myalgia, muscle pain and musculoskeletal pain appear nowhere in the current US prescribing information, including in the table of reactions reported in at least 2% of patients. The same is true of the Mounjaro label, which covers the identical molecule.

Does Zepbound cause muscle loss?

Weight loss does, and Zepbound causes a lot of weight loss. In the SURMOUNT-1 DXA substudy, lean mass fell 10.9% over 72 weeks on tirzepatide and 2.6% on placebo, but in both groups about 25% of the weight lost was lean tissue. The proportion did not differ, so the drug is not preferentially taking muscle.

Is 25% of weight loss as lean mass a normal amount?

It is close to the benchmark researchers use. The 2026 Annals of Internal Medicine review applied a benchmark of about 25% for fat-free mass measured by DXA or bioelectrical impedance, and found the median across incretin studies was 28.3%, with about two thirds above the benchmark. It also noted that nearly half of the non-drug weight loss comparisons exceeded it too.

Will protein and resistance training protect my muscle?

That is the standard recommendation and it is being tested rather than settled. A protocol for a randomised trial of resistance exercise and protein during semaglutide and tirzepatide treatment was published in 2026, which tells you the question is still open. Discuss specifics with your clinician or a registered dietitian, and bear in mind new training is itself a common cause of the aching that brought you here.

Is muscle pain the same question as joint pain?

No, and it is worth being precise with your prescriber about which you have. Joint pain is arthralgia, muscle pain is myalgia, and neither is on the Zepbound label. We cover the joint version, including a randomised trial that points the other way, in does Zepbound cause joint pain.

Should I stop Zepbound because my muscles hurt?

That is a decision for your prescriber. Do not start, stop or change a prescribed dose on the basis of a web page.

Related reading

Sources

This page summarises published prescribing information and peer-reviewed trials for general education. It is not medical advice, it contains no dosing guidance, and it cannot tell you what is causing your symptoms. Severe muscle pain, muscle weakness, dark urine or pain with fever should be assessed by a clinician without delay. Never start, stop or change a prescribed medicine on the basis of a web page.

Jabby is free on the App Store and keeps dose history and symptom logs in one record you can show your prescriber.

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