Yes. Thyroid medicine can sometimes cause heart palpitations, particularly when the amount of thyroid hormone in the body becomes higher than needed. Palpitations may feel like your heart is racing, pounding, fluttering, skipping beats or beating irregularly. Levothyroxine, a commonly used thyroid hormone replacement medicine, is known to cause cardiovascular effects including palpitations, a faster heart rate and heart rhythm disturbances when thyroid hormone replacement is excessive. (nhs.uk)
Palpitations do not automatically mean that your thyroid medicine is the cause or that something dangerous is happening. Stress, lack of sleep, caffeine, nicotine, other medicines, an overactive thyroid and heart rhythm problems can also cause them. (nhs.uk)
If palpitations started after beginning thyroid treatment, after a dose or product change, or are becoming more frequent, speak to your doctor or pharmacist. Do not stop or change prescription thyroid medicine on your own unless a healthcare professional tells you to do so. For broader information about treatment-related effects, see our related parent guide and the Chronic Medication Side Effects hub.
How thyroid Medicine Heart Palpitations can be linked to medicines or supplements
Thyroid hormones affect many processes in the body, including heart rate. When there is more thyroid hormone activity than your body needs, symptoms can resemble those of an overactive thyroid. These may include a fast or irregular heartbeat, sweating, anxiety, tremor, difficulty sleeping, heat intolerance and weight loss. (nhs.uk)
With levothyroxine, the NHS notes that most side effects occur when the dose is too high and may improve after the dose has been professionally adjusted. Regular blood tests are therefore used to check whether the prescribed dose is appropriate. (nhs.uk)
Heart symptoms deserve particular attention in older adults and people who already have cardiovascular disease. Current levothyroxine prescribing information warns that overtreatment can increase heart rate and may precipitate angina or arrhythmias, especially in these groups.
Timing clues
The timing of your symptoms can give your healthcare professional useful information, although timing alone cannot prove that the medicine caused the palpitations.
Tell your doctor or pharmacist if the palpitations began shortly after starting thyroid medicine, appeared after a change in dose or brand, became more noticeable after a change in how you take the medicine, or occur alongside symptoms such as shaking, sweating, unusual anxiety, heat intolerance, diarrhoea or difficulty sleeping. These accompanying symptoms can occur when thyroid hormone effects are excessive. (nhs.uk)
It is also important to mention any recent changes in other medicines, vitamins and supplements. Levothyroxine can interact with several medicines and products, while calcium and iron supplements can affect its absorption. Biotin can interfere with thyroid blood tests and make laboratory results harder to interpret accurately. (nhs.uk)
Medicines and product categories that may be associated with this symptom
Levothyroxine: Palpitations, tachycardia and arrhythmias are recognised cardiovascular adverse effects of excessive thyroid hormone replacement. (FDA Access Data)
Liothyronine or other T3-containing thyroid treatment: Rapid or irregular heartbeat is also a recognised serious adverse effect of liothyronine. (MedlinePlus)
Desiccated thyroid products: These contain thyroid hormones, including T3. UK medicines guidance notes that desiccated thyroid extract can produce hyperthyroid effects and is associated with risks including arrhythmia. (SPS – Specialist Pharmacy Service)
Iodine-containing supplements: Iodine is necessary for thyroid hormone production, but supplements can influence thyroid function and can interact with some medicines used for thyroid disease. Do not assume that a product marketed for “thyroid support” is automatically appropriate alongside prescribed treatment. Tell your healthcare professional about any iodine or other thyroid-related supplement you use. (ODs)
Caffeine-containing products: Coffee, energy drinks and other sources of caffeine can cause palpitations independently of thyroid treatment. If several possible triggers are present, a doctor may need to assess the overall pattern rather than attributing the symptom to one product. (nhs.uk)
The same principle applies to prescription medicines, over-the-counter products, herbal remedies, vitamins and supplements. Keep your doctor or pharmacist informed about everything you take rather than trying to identify the cause by stopping products one at a time without advice.
Red flags: when this symptom may need urgent medical attention
Many episodes of palpitations are not dangerous, but certain accompanying symptoms require urgent assessment. Seek immediate medical help if you currently have palpitations that do not go away, particularly if you also have:
- chest pain or significant chest discomfort;
- shortness of breath or difficulty breathing;
- feeling faint, severe dizziness or actual fainting;
- a seizure, collapse or loss of consciousness;
- swelling of the face, tongue or throat, difficulty swallowing, or other signs of a severe allergic reaction. (nhs.uk)
If these symptoms occurred but have now stopped, you should still obtain prompt medical advice. Do not drive yourself if you are faint, severely short of breath or otherwise medically unstable.
You should also arrange medical assessment if palpitations keep returning, are becoming more frequent, last more than a few minutes, or occur when you have an existing heart condition or significant family history of heart problems. (nhs.uk)
What to track before speaking to a doctor or pharmacist
What to track
Write down when the palpitations started and what they feel like. Note whether the heartbeat seems fast, pounding, fluttering or irregular, how long each episode lasts, how often it happens and what you were doing immediately beforehand.
Record the exact thyroid medicine, strength and prescribed dose you take. Mention any recent change in dose, formulation or brand and whether you have accidentally taken more medicine than prescribed. If you have taken an excessive dose, contact a healthcare professional promptly rather than waiting for symptoms to develop. (nhs.uk)
Also tell your healthcare professional about symptoms that happen around the same time, including shaking, sweating, diarrhoea, heat intolerance, insomnia, nervousness, unexplained weight change, breathlessness, dizziness or chest discomfort. (FDA Access Data)
Bring a complete list of prescription medicines, pharmacy products, vitamins, herbal remedies and supplements. Include calcium, iron, biotin, iodine-containing products and caffeine-containing supplements where relevant. This can help your doctor or pharmacist identify potential interactions or factors that may be affecting thyroid treatment.
Your clinician may consider your symptoms together with thyroid blood tests and, when appropriate, tests of your heart rhythm such as an ECG. Palpitations have many possible causes, so symptoms alone cannot establish whether your thyroid medicine is responsible. (nhs.uk)
What not to do without medical advice
What not to change without advice
Do not stop taking prescribed thyroid medicine simply because you experience palpitations. Do not halve the dose, skip doses, take doses on alternate days or switch thyroid products unless your prescriber has advised you to do so.
For levothyroxine, the NHS specifically advises people experiencing side effects to continue taking their medicine unless they are advised to stop. Thyroid blood tests are used to determine whether treatment needs adjustment. (nhs.uk)
Do not double a levothyroxine dose to compensate for a missed dose. (nhs.uk)
It is also unwise to add a “thyroid support”, iodine or other supplement in an attempt to correct your symptoms yourself. Supplements may influence thyroid function, interact with treatment or interfere with laboratory testing. (ODs)
If you are pregnant, have an existing heart condition, are an older adult, or the person experiencing symptoms is a child, discuss new or persistent palpitations with the treating healthcare professional because treatment and monitoring need to be individualised. (nhs.uk)
Related side-effect guides and reporting options in South Africa
Related symptom guides
If you are trying to understand whether another symptom could be medicine-related, browse the side effect symptoms A-Z. You can also explore the wider medication side effects library.
A suspected side effect can also be reported in South Africa. SAHPRA’s Med Safety system allows members of the public as well as healthcare professionals to report suspected adverse drug reactions. Reporting a suspected reaction does not prove that a medicine caused it, but reports contribute to medicine-safety monitoring. (Medsafety)
Find out how to report side effects in South Africa. SAHPRA’s current adverse-drug-reaction reporting guideline is Version 4, updated 23 October 2025. (Sahpra)
Frequently asked questions
Is this a common side effect?
Heart palpitations are a recognised effect of excessive thyroid hormone treatment, but they should not simply be regarded as an expected symptom that everyone taking thyroid medicine will experience. Current levothyroxine information lists palpitations, tachycardia and arrhythmias among cardiovascular adverse reactions associated particularly with excessive replacement. (FDA Access Data)
If palpitations are new, persistent or bothersome, discuss them with your doctor or pharmacist.
How long can heart palpitations last?
An individual episode of palpitations may last seconds, minutes or longer. (nhs.uk) How long medicine-related palpitations continue overall depends on their cause, so there is no reliable single timeframe that applies to everyone.
If they repeatedly return, are becoming more frequent or last longer than a few minutes, arrange medical assessment rather than waiting indefinitely for them to disappear. (nhs.uk)
Should I stop my thyroid medicine?
Do not stop, reduce or otherwise change prescribed thyroid medicine without professional advice unless you are receiving emergency instructions from a healthcare professional. With levothyroxine, side effects may indicate that the dose needs review, but that decision should be based on your clinical situation and appropriate testing. (nhs.uk)
Contact your doctor or pharmacist and explain what you are experiencing.
When should I seek help?
Seek immediate medical care for ongoing palpitations accompanied by chest pain, shortness of breath, feeling faint or fainting. Severe breathing difficulty, swelling of the face or throat, seizures or collapse also require emergency assistance. (nhs.uk)
For palpitations without emergency symptoms, arrange medical advice if they keep returning, are becoming more frequent, last more than a few minutes or concern you—especially if you have an existing heart condition. (nhs.uk)
This information is for general education and does not diagnose the cause of heart palpitations or replace advice from a doctor or pharmacist. Thyroid treatment should be reviewed using your individual symptoms, medical history, medicines and appropriate laboratory results.