Levothyroxine overdose can cause a racing or irregular heartbeat, shaking, anxiety, sweating, vomiting, diarrhea, or confusion. Call your local emergency number now for chest pain, trouble breathing, fainting, a seizure, loss of consciousness, or a very fast or irregular heartbeat. If you or a child took more than prescribed—even without symptoms—contact a poison center or urgent medical professional promptly, because symptoms may take days to appear.
When should you call emergency services?
Get emergency medical help immediately if someone who may have taken too much levothyroxine develops chest pain, breathing difficulties, a seizure, or signs of collapse. Mayo Clinic also identifies changes in consciousness, confusion, a fast or weak pulse, sudden loss of coordination, and sudden slurred speech as overdose warning signs requiring emergency attention.
- Chest pain, tightness, or discomfort.
- Difficulty breathing or unusually labored breathing.
- A very fast or irregular heartbeat, especially with dizziness or faintness.
- Fainting, collapse, or difficulty waking the person.
- Seizures or sudden changes in awareness.
- Sudden confusion, slurred speech, or loss of coordination.
Do not drive yourself to the hospital if you have emergency symptoms. Call your local emergency number and follow the dispatcher's instructions. If the overdose was intentional or involved a potentially large amount, seek urgent emergency assistance even if symptoms have not started.
What are the symptoms of levothyroxine overdose?
Levothyroxine replaces thyroid hormone and helps regulate several body functions. Taking too much can cause effects associated with excess thyroid hormone. According to MedlinePlus, symptoms of thyroid medicine overdose can affect the heart, digestive system, muscles, and nervous system.
- Heart symptoms: A racing, pounding, or irregular heartbeat, or palpitations (a noticeable awareness of your heartbeat).
- Nervous system symptoms: Anxiety, nervousness, agitation, irritability, shaking or tremors, and difficulty sleeping.
- Digestive symptoms: Nausea, vomiting, diarrhea, or stomach discomfort.
- Other symptoms: Excessive sweating, headache, muscle aches or cramps, and unusual restlessness.
- More concerning effects: Confusion, disorientation, seizures, loss of consciousness, or collapse.
These symptoms are examples of possible effects, not a checklist for deciding whether an overdose has occurred. Some symptoms can also have other causes. The amount taken, the person's medical history, current medicines, and the timing of the exposure all matter when a healthcare professional assesses the situation.
Can symptoms appear hours or days after an overdose?
Yes. A person may initially feel well after taking too much levothyroxine. Poison Control explains that overdose symptoms may take several days to appear. MedlinePlus notes that symptoms can sometimes be delayed for up to a week or develop gradually. Therefore, feeling normal immediately after taking extra tablets does not reliably show that the exposure is harmless.
If you know or suspect that more levothyroxine than prescribed was taken, seek professional advice promptly rather than waiting for symptoms. Tell the healthcare professional when the medicine was taken and how much may have been swallowed, even if the amount is uncertain.
What should you do if you take too much levothyroxine?
The appropriate response depends on how much was taken and the person's circumstances. The NHS advises getting medical advice after taking more than the prescribed dose. Although an extra dose is unlikely to cause problems in many cases, excess levothyroxine can sometimes be dangerous, so individual guidance is important.
Contact a local poison information service, pharmacist, or urgent medical service promptly for advice. If the amount is large or unknown, a child may have swallowed the medicine, or the overdose was intentional, seek immediate professional help. Use emergency services for any emergency symptoms described above.
What information should you have ready?
When speaking with a poison specialist or healthcare professional, try to provide:
- The medicine's name and tablet strength, as shown on the packaging.
- The number of tablets or estimated amount taken.
- The time the medicine was taken, including whether extra doses were taken over several days.
- The person's age and approximate weight, particularly if a child is involved.
- Any symptoms, existing medical conditions, and other medicines the person uses.
Keep the medicine packaging available and bring it to the hospital if advised to attend. MedlinePlus recommends seeking medical help promptly and not making someone vomit unless a poison specialist or healthcare professional specifically instructs you to do so.
Do not try to counteract the overdose with other medicines, home remedies, or additional doses. Ask a healthcare professional what to do about the next scheduled levothyroxine dose. Do not double doses or make lasting changes to your prescribed treatment without appropriate guidance.
What if your prescribed dose may be too high?
An overdose can involve taking extra tablets at once, but symptoms can also develop when a prescribed dose is higher than needed over time. For example, persistent palpitations, anxiety, sweating, difficulty sleeping, or diarrhea may warrant a medication review. Contact your prescribing clinician or pharmacist promptly if these symptoms begin or worsen, particularly after a dose change.
Seek emergency care for chest pain, breathing difficulties, fainting, a seizure, or other serious warning signs. For ongoing symptoms without emergency features, your clinician can review your dose, symptoms, medical history, and thyroid blood-test results to determine whether an adjustment or further assessment is needed. Do not stop levothyroxine permanently or change your treatment schedule on your own.
How can you reduce the risk of an accidental overdose?
Simple medication habits can reduce the chance of taking an extra dose by mistake. Keep levothyroxine in its original, clearly labelled container, store it out of children's reach, and use a written record or pill organiser if you have trouble remembering whether you have taken it. Check the tablet strength whenever a prescription is dispensed or the dose changes.
Do not take an extra tablet to make up for a missed dose unless a healthcare professional has advised you to do so. If you cannot remember whether you took your medicine, ask your pharmacist or prescribing clinician for instructions instead of guessing.