Mounjaro Side Effects: Hair Loss, Tiredness, Constipation and How Long They Last

In placebo-controlled trials in adults with type 2 diabetes, seven side effects were reported by at least 5% of people on Mounjaro: nausea, diarrhea, decreased appetite, vomiting, constipation, indigestion (dyspepsia) and abdominal pain.1

Source: Mounjaro label, Table 1, pool of two placebo-controlled trials (SURPASS-1 and SURPASS-5).1

Overall, gastrointestinal side effects affected 37.1% to 43.6% of people on Mounjaro, rising with dose, against 20.4% on placebo.1 Between 3.0% and 6.6% stopped Mounjaro because of them, against 0.4% on placebo.1 Other effects reported more often than on placebo include burping, gas, acid reflux and bloating.1

Injection site reactions were reported by 3.2% of people on Mounjaro, against 0.4% on placebo.1 Mounjaro can also raise the heart rate by an average of 2 to 4 beats per minute.1

Hair loss (alopecia) is listed in the Mounjaro label among side effects reported since approval, not among its common side effects.1 Because those reports are voluntary, the label says their frequency cannot be reliably estimated.1

The Zepbound label, which tested the same drug at the same doses for weight loss, gives numbers. In its two 72-week trials, hair loss was reported by 4% to 5% of people on tirzepatide, against 1% on placebo.2 The label links it to weight reduction.2

In the Zepbound trials, hair loss was far more common in women: 7.1% of women on tirzepatide reported it, against 0.5% of men.2 No one on tirzepatide in those trials stopped treatment because of hair loss.2

Shedding linked to large weight loss usually grows back. The American Academy of Dermatology names losing 20 pounds or more as a trigger for excessive shedding, says it usually starts a few months after the trigger, and says hair tends to regain its normal fullness within six to nine months.3

The label has no specific advice on how to stop hair loss on Mounjaro. If shedding is heavy, lasts, or comes in patches, a dermatologist can check for other causes.3

Fatigue is not among the side effects most commonly reported in Mounjaro's placebo-controlled trials, but it was reported by 10% of people in a large cardiovascular outcomes trial of Mounjaro.1 That trial followed 6,647 adults with type 2 diabetes and heart disease on Mounjaro.1

In the Zepbound weight-loss trials, fatigue was reported by 5% to 7% of people on tirzepatide, against 3% on placebo.2 That figure groups fatigue, weakness (asthenia), lethargy and malaise.2

The label does not give a cause for fatigue. It does name situations that can leave people drained. Low blood sugar is more likely when Mounjaro is combined with insulin or a sulfonylurea.1 Vomiting and diarrhea can lead to dehydration.1 Mounjaro also reduces how much people eat; decreased appetite was reported by up to 11%.1 Persistent tiredness is worth raising with your prescriber.

Yes. Constipation was reported by 6% to 7% of people on Mounjaro, against 1% on placebo.1 It was more common in the cardiovascular outcomes trial, at 13%.1 In the Zepbound weight-loss trials, 11% to 17% reported constipation, against 5% on placebo.2

Since approval, severe constipation including fecal impaction, as well as intestinal blockage (ileus and intestinal obstruction), has been reported.1

Tirzepatide slows how fast the stomach empties.1 The Zepbound label adds that this delay is largest after the first dose and lessens over time.2 The label does not give a separate mechanism for constipation.

The label does not report how long constipation lasts. It does say that most nausea, vomiting and diarrhea occurred during dose escalation and decreased over time.1 Constipation that is severe or does not improve should be reported to a prescriber.

Headache is not listed among the common side effects in the Mounjaro label or the Zepbound label.1,2 Neither label describes what a headache on tirzepatide feels like. A headache that is severe, sudden or does not go away should be checked by a clinician.

For most people, nausea, vomiting and diarrhea are temporary: the label says most of these happened during dose escalation and decreased over time.1 That is why Mounjaro starts at 2.5 mg and rises only after at least 4 weeks on each dose.1

The label does not give a fixed number of days. Tirzepatide has a half-life of about 5 days and reaches its peak 8 to 72 hours after an injection, so each dose stays active for most of the week.1 Side effects that are severe or do not go away should be reported, because fluid loss from vomiting or diarrhea can lead to kidney injury.1

Our Mounjaro dosage guide explains the step-up schedule, and our Zepbound side effects guide covers the weight-loss trials in more depth.

Mounjaro carries a boxed warning: tirzepatide caused thyroid C-cell tumors in rats, and it is unknown whether it causes them, including medullary thyroid carcinoma (MTC), in humans.1 Mounjaro must not be used by people with a personal or family history of MTC or with Multiple Endocrine Neoplasia syndrome type 2.1

The label's other warnings are:1

• Acute pancreatitis. Stop Mounjaro and seek care for severe stomach pain that may spread to the back.
• Low blood sugar when used with insulin or a sulfonylurea.
• Serious allergic reactions, including anaphylaxis and angioedema.
• Acute kidney injury from fluid loss due to vomiting or diarrhea.
• Severe gastrointestinal reactions. Mounjaro is not recommended in severe gastroparesis.
• Diabetic retinopathy complications in people with a history of retinopathy.
• Gallbladder disease, reported by 0.6% of people on Mounjaro and 0% on placebo.
• Pulmonary aspiration during anesthesia or deep sedation. Tell your care team before any procedure.
• Never share a KwikPen, even with a new needle.

Severe gastrointestinal reactions affected 0.4% to 1.3% of people on Mounjaro, against 0.9% on placebo.1 Our safety hub gathers these warnings across GLP-1 drugs.

Can Mounjaro make you tired in the first weeks? The label does not report when fatigue starts. Most stomach side effects were reported while the dose was being raised.1

Does Mounjaro have fewer side effects than Ozempic? The labels report different trials, and the Mounjaro label notes that rates from different trials cannot be compared directly.1 Our Mounjaro vs Ozempic comparison lays out what each label reports.

Can Mounjaro affect birth control pills? Yes. The label advises a non-oral method, or adding a barrier method, for 4 weeks after starting and after each dose increase.1

Does Mounjaro cause low blood sugar? On its own, low blood sugar was uncommon in the trials. The risk rises when Mounjaro is combined with insulin or a sulfonylurea.1

Side effects often decide which drug and dose people stay on. Compare the two tirzepatide brands in Mounjaro vs Zepbound, check prices in our Mounjaro cost guide, or browse our best GLP-1 options. Before you start, read how to inject Mounjaro.

This article is for information only and is not medical advice. Report side effects to your prescriber, and seek urgent care for severe stomach pain, signs of an allergic reaction, or a lump in the neck. Mounjaro is a prescription drug with real risks and side effects.