How tirzepatide interacts with cardiac drugs
Tirzepatide doesn’t go through the liver enzymes that handle most antiarrhythmics, so direct chemical interactions aren’t expected.
The Mounjaro SmPC (the regulatory document for prescribers) states that tirzepatide delays gastric emptying and can lower the peak blood level of oral drugs taken at the same time.
The effect is strongest when you first start tirzepatide or after a dose increase, then settles.1
For most oral cardiac drugs, this delay is small enough that overall absorption stays the same.
A 2024 systematic review of GLP-1 receptor agonists and oral medications concluded that dose adjustments are probably not needed in most cases, though the authors flagged drugs with a narrow therapeutic index for closer attention.3
The SmPC names warfarin and digoxin specifically and recommends monitoring at the start of treatment and after each dose increase.1
If you’re taking other medications alongside Mounjaro, our GLP-1 medication compatibility checker covers the most common combinations.
If you have heart failure as well
Many people on rate-control or rhythm-control medication also have heart failure, particularly heart failure with preserved ejection fraction (HFpEF).
The SUMMIT trial, published in the New England Journal of Medicine in 2024, found that tirzepatide reduced the combined risk of cardiovascular death and worsening heart failure events in adults with HFpEF and obesity.4 This doesn’t change the drug-interaction guidance for the rate or rhythm-control medications covered below.
Beta-blockers
Beta-blockers are first-line for rate control in atrial fibrillation, according to NICE NG196 and the 2024 ESC AF guidelines.2,5
Common UK options include bisoprolol, metoprolol, atenolol, nebivolol, and carvedilol.
There’s no known direct interaction between tirzepatide and any beta-blocker.
The 2024 systematic review of GLP-1 oral drug interactions didn’t flag this drug class as a concern.3
Beta-blockers can blunt the early symptoms of low blood sugar, like a fast heartbeat and trembling.
If you’re taking Mounjaro for type 2 diabetes alongside another glucose-lowering drug, your GP should mention this when you start the beta-blocker. Sweating tends to remain a reliable warning sign.
Tirzepatide is associated with a small increase in resting heart rate, averaging around 1.8 beats per minute across studies.6 Your beta-blocker usually offsets this.
As you lose weight, you may also find your blood pressure and resting heart rate fall, sometimes enough that your prescriber will want to review your beta-blocker dose.
Digoxin
Digoxin is the antiarrhythmic that requires the most careful attention when taking Mounjaro.
It has a narrow therapeutic window, meaning the gap between a level that controls your symptoms and one that causes side effects is small.3
The Mounjaro SmPC explicitly recommends monitoring people on digoxin at the start of treatment and after each tirzepatide dose increase.1
The reason for this extra monitoring is the effect on gastric emptying. Tirzepatide can slow the rate at which digoxin reaches peak blood levels, particularly when you first start it.
The 2024 systematic review found that digoxin levels stayed within the therapeutic range across studies, but the authors still recommend monitoring at the start of co-treatment.3
In practice, ask your GP or cardiologist to check your digoxin level when you start Mounjaro, and again after each dose increase.
Symptoms suggesting a high digoxin level include nausea, loss of appetite, blurred vision, or seeing yellow or green halos around lights. Mention these to your GP straight away.
Amiodarone
Amiodarone is used for harder-to-control rhythm problems, including some forms of atrial fibrillation and ventricular arrhythmias. There’s no published direct interaction between amiodarone and tirzepatide.
The consideration here isn’t a direct drug interaction; it’s the effect amiodarone has on the thyroid.
Amiodarone affects thyroid function in roughly 5 to 15% of people who take it long-term, causing either an under- or overactive thyroid.7
Significant weight loss can also change how much thyroid hormone replacement you need if you’re already on levothyroxine.
Together, this means your thyroid function tests may shift as you lose weight on Mounjaro.
Your GP would normally check thyroid function every six months on amiodarone, and it’s recommended to maintain this frequency.
If amiodarone has affected your thyroid and you’re on levothyroxine, see our Mounjaro with levothyroxine guide for how the dose may change as you lose weight.
Amiodarone also affects liver function and can prolong the QT interval (a measurement of how long the heart’s electrical signal takes to recover between beats).
Tirzepatide hasn’t been shown to prolong QT, so the combination doesn’t add to that risk.1
One practical food point worth knowing: grapefruit juice meaningfully increases amiodarone blood levels and can prolong QT further. This is true whether or not you take Mounjaro, but it’s worth flagging because Mounjaro can change what people eat and drink. Avoid grapefruit and grapefruit juice while on amiodarone.
Dronedarone
Dronedarone is a second-line option for maintaining sinus rhythm after cardioversion in non-permanent atrial fibrillation.
NICE recommends it through technology appraisal TA197, and it’s typically initiated by a cardiologist rather than a GP.8
There’s no published direct interaction between tirzepatide and dronedarone. The 2024 systematic review of GLP-1 oral drug interactions didn’t flag this drug.3
Dronedarone has its own monitoring requirements that continue as usual.
Liver function tests are recommended in the first six months of treatment because of rare cases of severe liver injury, and ECG checks track QT prolongation.
Tirzepatide doesn’t affect QT and isn’t known to meaningfully affect liver function, so it doesn’t add to either monitoring need.
One important caveat: dronedarone is contraindicated in people with permanent AF, advanced heart failure, or recent decompensated heart failure.
If your AF has become permanent or your heart failure has worsened since dronedarone was started, your cardiologist will already be reviewing it. Mention you’re considering Mounjaro at that review.
If you’re also on digoxin, dronedarone independently raises digoxin levels by roughly 1.7 to 2.5 times.
The digoxin monitoring point in the Digoxin section above takes priority for that combination, whether or not Mounjaro is included.
Flecainide and sotalol
Flecainide is used for paroxysmal atrial fibrillation in people with structurally normal hearts. Its absorption isn’t strongly food-dependent, and there are no published interactions with tirzepatide.
Flecainide is mainly cleared by the kidneys. If your kidney function changes as you lose weight, your cardiologist may want to have your kidney function checked to confirm the dose is still right for you. This is the routine review most people on flecainide get anyway.
Sotalol is used for both rate and rhythm control. It’s a beta-blocker with extra activity on the heart’s electrical system.
Its main safety concern is dose-dependent QT prolongation, which is monitored with regular ECGs, whether or not you’re on Mounjaro.
Tirzepatide doesn’t affect QT, so it doesn’t add to this concern.1 Sotalol is also cleared by the kidneys, so the same kidney monitoring point applies as with flecainide.
Verapamil and diltiazem
Verapamil and diltiazem are calcium channel blockers used as an alternative to beta-blockers for rate control in atrial fibrillation.2,5
NICE NG196 lists them alongside beta-blockers as initial options if a beta-blocker isn’t suitable.5
There’s no published interaction between tirzepatide and either drug.
They’re absorbed orally, so the gastric emptying point applies in theory, but their therapeutic windows are wide enough that small changes in absorption don’t usually cause problems.
You can keep taking your usual dose at the usual time. If you also take digoxin alongside verapamil (a combination sometimes used in AF), the digoxin monitoring point above takes priority, since verapamil can independently raise digoxin levels.
What monitoring you’ll need
The plan depends on which antiarrhythmic you’re on. Most checks overlap with reviews you’d already have.
Before starting Mounjaro
- Current weight, BMI, and blood pressure
- Kidney and liver function
- Thyroid function (especially if you’re on amiodarone)
- Digoxin level if you’re on digoxin
- A medication review to confirm that everything you take is current
After starting and at each dose increase
Mounjaro doses increase gradually, from 2.5 mg through 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg, with at least 4 weeks between increases.
When increasing your dose, keep an eye on the following:
- For digoxin: a level check at the start of Mounjaro and after each dose increase, in line with the SmPC1
- For amiodarone: thyroid function tests on your usual six-monthly cycle
- For dronedarone: continue routine liver function tests and ECG checks at the intervals your cardiologist sets
- For warfarin (if you take one alongside): more frequent INR checks at the start, as your usual anticoagulation service would manage
- For everyone: a routine review of weight, blood pressure, and resting heart rate
What weight loss may mean for your dose
Meaningful weight loss often changes the amount of rate-control or blood pressure medication someone needs.
Lower body weight typically means lower resting heart rate and blood pressure to manage, so beta-blocker, calcium channel blocker, and antihypertensive doses may all need a downward review over the course of a year.
Tell your GP or cardiologist straight away if you notice palpitations, fainting, dizziness, severe nausea, vomiting that prevents you from keeping medication down, or any new heart symptoms.
Drug-class summary
The table below summarises what’s known about each cardiac drug class in relation to Mounjaro. None of these is an absolute contraindication.
| Drug class |
Examples |
Known interaction with tirzepatide |
Practical point |
| Beta-blockers |
Bisoprolol, metoprolol, atenolol, nebivolol, carvedilol |
None reported3 |
May mask hypoglycaemia symptoms in type 2 diabetes; dose may come down with weight loss |
| Digoxin |
Digoxin |
Monitor levels at initiation and dose increases1 |
Narrow therapeutic window; SmPC-flagged drug |
| Amiodarone and sotalol |
Amiodarone, sotalol |
None reported3 |
Continue routine thyroid (amiodarone) and ECG (sotalol) checks; avoid grapefruit with amiodarone |
| Dronedarone |
Dronedarone |
None reported3 |
Continue routine liver function and ECG monitoring; raises digoxin levels independently |
| Flecainide |
Flecainide |
None reported3 |
Cleared by the kidneys, so check kidney function at routine reviews |
| Calcium channel blockers (rate-control type) |
Verapamil, diltiazem |
None reported3 |
Wide therapeutic window; usual dose at usual time |
Common questions
Will Mounjaro affect my beta-blocker?
No published interaction has been reported between tirzepatide and any beta-blocker.3 You can take your usual dose at the usual time.
If you have type 2 diabetes, remember that beta-blockers can mask the early symptoms of low blood sugar.
Can Mounjaro change my digoxin level?
Possibly, especially when you first start Mounjaro or move up a dose. The Mounjaro SmPC names digoxin as a drug to monitor at initiation and after each dose increase, because tirzepatide can slow gastric emptying.1
Ask your GP about a digoxin level check at these points.
What about amiodarone?
There’s no direct drug interaction. Monitor thyroid function, as amiodarone can independently affect it, and weight loss can also affect it.
Continue your usual six-monthly thyroid tests, and tell your GP if you notice symptoms such as fatigue, a racing heart, or sensitivity to temperature. Avoid grapefruit and grapefruit juice while on amiodarone.
Will my heart rate change on Mounjaro?
Tirzepatide raises resting heart rate by around 1.8 beats per minute on average.6
If you’re on a beta-blocker or rate-control medication, this is usually offset.
If you notice persistent palpitations or a higher resting rate at home, mention it to your GP or cardiologist.
Do I need an ECG when starting Mounjaro?
For most people, no. Tirzepatide doesn’t prolong the QT interval or directly affect the heart’s electrical signal.1
If you’re on a QT-prolonging drug like sotalol, amiodarone, or dronedarone, you’ll already have ECGs scheduled at your usual review intervals. Those continue as planned.
Is Mounjaro safe if I have a pacemaker or implantable defibrillator?
Yes. Tirzepatide is a subcutaneous medication and doesn’t interact with implanted cardiac devices.
Your device’s monitoring schedule continues as usual.
If you notice changes in how the device feels or new symptoms, contact your cardiac device team rather than stopping Mounjaro.
Should I have my levels checked when I start Mounjaro?
For digoxin and warfarin, yes, in line with the Mounjaro SmPC.1
For other heart rhythm medications, routine kidney function, liver function, and ECG checks at your usual review intervals are usually enough. Your prescriber will set the schedule.
Can I take Mounjaro if I have atrial fibrillation?
For most people, yes. The 2024 ESC AF guidelines highlight obesity as a modifiable risk factor for AF, and weight loss reduces AF burden.2 See our Mounjaro with atrial fibrillation guide for more on the condition.
What if I’m sick or vomiting?
Severe vomiting can stop you from keeping oral antiarrhythmics down, which is more concerning for narrow-window drugs like digoxin or flecainide.
If you vomit within an hour of taking a tablet, don’t double-dose; speak to your GP or pharmacist about whether to retake it.
Contact your GP or 111 the same day if you can’t keep medication down for more than 24 hours, and earlier if you’re on digoxin or have new heart symptoms.
Take home message
You can take Mounjaro alongside the cardiac drugs commonly used for heart rhythm problems. Direct chemical interactions aren’t expected.
Digoxin requires the most attention due to its narrow therapeutic window, and the Mounjaro SmPC specifically recommends monitoring at the start and after each dose increase.
For other heart rhythm drugs, routine cardiology and primary care reviews usually cover what’s needed.
Tell your GP and cardiologist about every medication you take, including Mounjaro, so they can plan checks together.
Meaningful weight loss often reduces the amount of rate-control or blood pressure medication someone needs. Expect this as a review point over the first six to twelve months on Mounjaro.
If you’re on rate or rhythm-control medication, our health coaches and registered dietitians help you coordinate weight loss with your existing cardiac care.
They support members through dose changes, monitoring schedules, and the practical aspects of eating well alongside cardiac medication, which is particularly useful when appetite is reduced on Mounjaro.
A 2025 study published in JMIR Formative Research found that active subscribers on Second Nature’s GLP-1-supported programme lost an average of 19.1% of their body weight at 12 months, with 77.7% achieving at least 10% weight loss.9 The programme has worked with the NHS for over six years.
Second Nature's Mounjaro and Wegovy programmes
Second Nature provides Mounjaro or Wegovy as part of our Mounjaro and Wegovy weight-loss programmes.
Why choose Second Nature over other medication providers, assuming you're eligible?
Because peace of mind matters.
We've had the privilege of working with the NHS for over eight years, helping people across the UK take meaningful steps toward a healthier, happier life.
Our programmes are designed to meet people where they are, whether that means support with weight loss through compassionate one-to-one health coaching, or access to the latest weight-loss medications (like Mounjaro and Wegovy) delivered alongside expert care from a multidisciplinary team of doctors, psychologists, dietitians, and personal trainers.
At the heart of everything we do is a simple belief: real, lasting change comes from building better habits, not relying on quick fixes. We're here to support that change every step of the way.
With over a decade of experience, thousands of lives changed, and a long-standing record of delivering programmes used by the NHS, we believe we're the UK's most trusted weight-loss programme.
We hope to offer you something invaluable: peace of mind, and the support you need to take that first step.
References
- Eli Lilly. (2025). Mounjaro (tirzepatide) Summary of Product Characteristics. Electronic Medicines Compendium.
- Van Gelder, I.C. et al. (2024). 2024 ESC Guidelines for the management of atrial fibrillation. European Heart Journal, 45(36), 3314-3414.
- Calvarysky, B. et al. (2024). Drug-drug interactions between glucagon-like peptide 1 receptor agonists and oral medications: a systematic review. Drug Safety, 47(5), 439-451.
- Packer, M. et al. (2024). Tirzepatide for heart failure with preserved ejection fraction and obesity (SUMMIT). New England Journal of Medicine, 391(22), 2087-2098.
- National Institute for Health and Care Excellence. (2021). Atrial fibrillation: diagnosis and management (NG196).
- Yang, Y. et al. (2024). Impact of a dual glucose-dependent insulinotropic peptide/glucagon-like peptide-1 receptor agonist tirzepatide on heart rate among patients with type 2 diabetes: a systematic review and pairwise and network meta-analysis. Diabetes, Obesity and Metabolism, 26(2), 548-556.
- Bartalena, L. et al. (2018). 2018 European Thyroid Association (ETA) guidelines for the management of amiodarone-associated thyroid dysfunction. European Thyroid Journal, 7(2), 55-66.
- National Institute for Health and Care Excellence. (2010, updated 2012). Dronedarone for the treatment of non-permanent atrial fibrillation (TA197).
- Richards, R. et al. (2025). A remotely delivered GLP-1RA-supported specialist weight management program in adults living with obesity: retrospective service evaluation. JMIR Formative Research, 9(1), e72577.
