How the documents describe the heart rate rise
All three sets of product information record the effect, with slightly different figures. The US label reports the average change in SURMOUNT-1 and SURMOUNT-2; Canada pools three placebo-controlled weight trials; and Europe, where tirzepatide is sold as Mounjaro®, gives separate figures for weight management and sleep apnea trials and puts a raised heart rate in its common category, described in the patient leaflet as a fast pulse [1][3][4].
| Measure | Zepbound® or tirzepatide | Placebo | Source |
|---|---|---|---|
| Average rise, SURMOUNT-1 and -2 | 1 to 3 beats/min | No rise | US label §6.1 [1] |
| Average rise, three weight trials | 3 beats/min | 0 beats/min | Canadian monograph §8.2 [3] |
| Average rise, weight-management and sleep apnea pools | 3 and 2 beats/min | Under 1 beat/min | EU SmPC §4.8 [4] |
| Sustained rise over 20 beats/min, SURMOUNT-1 (5 / 10 / 15 mg) | 2.4% / 4.9% / 6.3% | 1.2% | EU SmPC §4.8 [4] |
| Arrhythmia and conduction events, SURMOUNT-1 (5 / 10 / 15 mg) | 3.7% / 3.3% / 3.3% | 3.6% | EU SmPC §4.8 [4] |
Average change versus how it feels
A rise of a few beats per minute is unlikely to be felt on its own. MedlinePlus describes palpitations as a sensation that the heart is pounding or racing, or skipping beats, felt in the chest, throat or neck, and notes that the rhythm may be normal or abnormal [11]. A normal resting rate is 60 to 100 beats per minute; above 100 is called tachycardia [11].
The SURMOUNT-1 figure for sustained rises over 20 beats per minute matters more for symptoms, because it shows a minority with a clearly bigger change, and that share grew with dose [4]. In the same trial, arrhythmia and conduction events were no more frequent on tirzepatide than on placebo, and changes in the PR interval on the ECG were small [4]. Canada reports no clinically meaningful PR or QTc differences in phase 3 trials, though no dedicated QT study was done for Zepbound® [3].
What rhythm studies show
Studies in people without diabetes fit Zepbound®’s main use best. A 2026 network meta-analysis of randomised trials in adults with overweight or obesity and no diabetes found every GLP-1-type medicine studied raised heart rate; for tirzepatide the estimate was about 2 beats per minute above placebo, with the size of the rise varying by dose [5]. A Bayesian meta-analysis of 10 tirzepatide trials in 6,515 people with overweight or obesity found no clear association with atrial fibrillation (odds ratio 2.20, credible interval 0.81 to 6.75); the odds of any arrhythmia were higher (1.84, 1.04 to 3.90), but events were rare and the authors urge caution [6].
Real-world reports add texture. An analysis of FDA reports about tirzepatide, mostly sent by consumers, found no link with atrial fibrillation or fast heart rate in reports from health professionals; a tachycardia signal seen among reports that recorded body weight was not reproduced when only professionals’ reports were analysed [7]. Two case reports stand out. A 28-year-old woman with obesity and postural orthostatic tachycardia syndrome saw her lying and standing heart rates rise by 20 to 30 beats per minute on tirzepatide prescribed for weight loss [8]. A 62-year-old woman developed new atrial fibrillation with palpitations and low blood pressure soon after starting tirzepatide, which did not recur after stopping [9]. Single cases cannot show cause or frequency.
Three other labelled reasons for a racing heart
When the heart races on Zepbound®, the medicine’s direct effect on rate is only one candidate. Three others are written into the Zepbound® information.
- Low blood sugar. Fast heartbeat, shakiness, sweating, hunger and feeling jittery are on the Medication Guide’s list of signs [2]. In SURMOUNT-2, readings below 54 mg/dL occurred in 4.2% on Zepbound® versus 1.3% on placebo, and in 10.3% of those also on a sulfonylurea [1].
- Dehydration. The label warns that vomiting and diarrhea can lead to dehydration [1], and MedlinePlus lists a rapid heartbeat among its signs [13]. Low blood pressure, recorded in 1.6% on Zepbound® against 0.1% on placebo, was also seen alongside stomach side effects and dehydration [1].
- Allergic reaction. If the heart is racing very fast and you also have a swollen face or throat, breathing difficulty, fainting or a severe rash, stop Zepbound® and get help immediately [2].
Sleep apnea, obesity and heart rhythm
Zepbound®’s sleep apnea trials enrolled adults with obesity and moderate to severe obstructive sleep apnea, two thirds or more of them men, and excluded people with type 2 diabetes [1]. In the European pooled sleep apnea data, average heart rate rose by 2 beats per minute on tirzepatide [4].
A 2026 review describes how obesity and sleep apnea together promote heart rhythm problems, particularly atrial fibrillation, through fat around the heart, low oxygen at night and strain on the autonomic nervous system. It suggests that tirzepatide, by reducing weight and sleep apnea severity, might indirectly lower arrhythmia risk, but that has not been tested [10]. For now, the practical point is that people taking Zepbound® for sleep apnea may have rhythm problems that predate the medicine.
Other causes of palpitations
MedlinePlus lists common causes that have nothing to do with Zepbound®: anxiety, stress or panic, caffeine, nicotine, too much alcohol, exercise, fever, diet pills, stimulant drugs and decongestant medicines such as phenylephrine or pseudoephedrine [11]. When an abnormal rhythm is behind the sensation, MedlinePlus points to heart or valve disease, an overactive thyroid, a potassium imbalance, low blood oxygen, and certain asthma, blood pressure or heart medicines [11].
Canada’s Zepbound® monograph adds a medicine-specific caution: combining it with other heart-rate-raising drugs, for example ones with sympathomimetic or anticholinergic activity, calls for care [3]. If you are unsure whether a cold remedy or other medicine falls into that group, ask your pharmacist.
What may help
The home measures MedlinePlus describes are simple: less caffeine, nicotine and other stimulants, practical ways of easing stress and anxiety, relaxation or breathing exercises, yoga, meditation or tai chi, regular exercise and no smoking [11]. After a serious cause has been ruled out, it suggests not monitoring every beat, while still reporting a sudden increase or a change in pattern [11].
For the Zepbound®-specific causes, the Medication Guide asks you to drink fluids to reduce the chance of dehydration, and, if you use insulin or a sulfonylurea, to agree a plan for low blood sugar with your provider before starting [2]. A note of your resting pulse at the time of an episode is useful information to bring.
Zepbound® and Mounjaro® are registered trademarks of Eli Lilly and Company. PepLabo is not affiliated with or endorsed by Eli Lilly and Company.
When to get help
The signs and contact information below come from this article’s sourced guidance.
Emergency
- Palpitations with chest pain, shortness of breath, fainting or reduced alertness, unusual sweating or dizziness
Contact: Emergency services (911 or local number)
MedlinePlus [11]
- Heart racing very fast together with a swollen face, lips or throat, difficulty breathing or a severe rash
Contact: Stop Zepbound® and get emergency help
Medication Guide [2]
Today
- Pounding heart plus shakiness, sweating, hunger or confusion, more so if you use insulin or a sulfonylurea
Contact: Follow your low blood sugar plan, then let your prescriber know
- Palpitations that are new or have changed, or a resting pulse above 100 with no exercise, fever or anxiety to explain it
Contact: Your health care provider right away
MedlinePlus [11]
- Fast heartbeat with ongoing vomiting or diarrhea, strong thirst or dizziness
Contact: Your prescriber, the same day (possible dehydration)