Yes. Thyroid medicine can sometimes be associated with anxiety, nervousness, restlessness or a racing heartbeat, particularly when thyroid hormone replacement such as levothyroxine produces more thyroid hormone effect than your body currently needs. Feeling anxious is listed as a common side effect of levothyroxine, and side effects are more likely when the dose is too high.
However, anxiety does not automatically mean your medicine is the cause. An overactive thyroid itself can cause anxiety, irritability, poor sleep, sweating, tremor and heart palpitations. Other medicines, supplements, caffeine, stress and unrelated health conditions may cause or worsen similar symptoms.
If you are concerned about thyroid medicine causing anxiety, do not change or stop a prescription thyroid medicine on your own. Keep track of your symptoms and speak to your doctor or pharmacist. They may need to consider your symptoms alongside your thyroid blood tests, current dose, other medicines and supplements.
You can also read our related parent guide for a broader overview of thyroid medication side effects.
How thyroid medicine anxiety can be linked to medicines or supplements
Thyroid hormones influence many processes in the body, including heart rate, temperature regulation, energy use and mood. When there is too much thyroid hormone activity, symptoms can resemble physical anxiety.
These symptoms may include:
- feeling anxious, nervous or unusually restless
- irritability
- difficulty sleeping
- a racing, pounding or irregular heartbeat
- shaking or trembling
- excessive sweating
- feeling unusually hot
- increased energy or feeling unable to settle
- unexplained weight loss
- more frequent bowel movements
These are also recognised symptoms of hyperthyroidism, which is why it may be difficult to tell from symptoms alone whether anxiety is being caused by the medicine, the underlying thyroid condition or something else.
Blood tests and a clinical assessment may be needed to understand what is happening.
Timing can provide useful clues
Think about when the anxiety began.
For example, tell your doctor or pharmacist if it appeared:
- after starting thyroid hormone treatment
- after a recent dose change
- after changing thyroid medicine products
- after accidentally taking more medicine than intended
- after starting or stopping another medicine or supplement
- alongside new palpitations, tremor, sweating or sleep problems
- after your usual routine for taking your thyroid medicine changed
This information does not prove that the medicine caused the anxiety, but it can help a healthcare professional decide what needs to be checked.
Medicines and product categories that may be associated with this symptom
Levothyroxine
Levothyroxine is a synthetic form of thyroid hormone commonly used to treat an underactive thyroid.
Feeling anxious, nervous or irritable, difficulty sleeping, tremor, sweating and palpitations can occur when the thyroid hormone effect is excessive. Official medicine information describes adverse effects of levothyroxine as resembling symptoms of hyperthyroidism when too much thyroid hormone is present.
This does not mean everyone who develops anxiety while taking levothyroxine has been prescribed the wrong dose. Anxiety has many possible causes, and thyroid hormone requirements can differ between people.
Other thyroid hormone preparations
Other medicines that supply thyroid hormone may also produce symptoms such as nervousness or anxiety when thyroid hormone activity becomes excessive. MedlinePlus lists anxiety, irritability, sleep problems and other hyperthyroid-type symptoms with some thyroid hormone preparations.
If you take a thyroid medicine other than levothyroxine, check the patient information leaflet supplied with your specific product and discuss unexpected symptoms with your pharmacist or doctor.
Medicines for an overactive thyroid
Medicines such as carbimazole are used to reduce excessive thyroid hormone production rather than replace thyroid hormone.
If you have recently started treatment for an overactive thyroid, anxiety or a racing heartbeat may sometimes still be related to the underlying hyperthyroidism, because treatment does not necessarily control symptoms immediately. NHS guidance notes that people may begin to feel better after one to three weeks of carbimazole, while the full effect can take longer.
Do not assume ongoing anxiety is either a medicine side effect or proof that the treatment is not working. Your clinician can assess your symptoms and thyroid results.
Iodine and thyroid-related supplements
Tell your healthcare professional about vitamins, minerals, herbal preparations and “thyroid support” products you use.
Iodine is necessary for thyroid hormone production, but high iodine intake can affect thyroid function. In susceptible people, excessive iodine intake can contribute to hyperthyroidism.
Some supplements and medicines can also affect how levothyroxine is absorbed. Calcium and iron are important examples, and clinicians may need to know how and when you take them when interpreting thyroid results or reviewing your treatment.
Do not start high-dose iodine or other thyroid-related supplements specifically to treat anxiety or thyroid symptoms without professional advice.
Red flags: when this symptom may need urgent medical attention
Anxiety on its own is not usually a medical emergency. However, seek urgent medical attention if anxiety or agitation occurs together with symptoms such as:
- chest pain or significant chest pressure
- a very fast or irregular heartbeat that is severe or persistent
- fainting or feeling as though you may faint
- severe shortness of breath
- a seizure
- severe confusion or extreme agitation
- a very high temperature with a rapid or irregular heartbeat and severe illness
- swelling of the face, lips, tongue or throat
- difficulty breathing or swallowing
- a widespread severe rash or other signs of a serious allergic reaction
Serious reactions to levothyroxine are uncommon, but official guidance identifies severe allergic reactions and severe symptoms associated with a sudden excess of thyroid hormone as reasons for urgent medical assessment.
If you are having thoughts of suicide or harming yourself, seek urgent professional help regardless of whether you believe thyroid medicine is responsible.
Pregnant people, children, older adults and people with heart disease should also seek medical advice promptly when new or significant symptoms develop rather than attempting to adjust thyroid treatment themselves.
What to track before speaking to a doctor or pharmacist
A short symptom record can make a medication review more useful.
Write down:
- the name and strength of your thyroid medicine
- your prescribed dose
- how long you have been taking it
- any recent dose or product changes
- when the anxiety first appeared
- whether it occurs continuously or at particular times
- whether you also have palpitations, tremor, sweating or insomnia
- any changes in weight or appetite
- all other prescription and non-prescription medicines you use
- vitamins, minerals and supplements, including iodine, calcium and iron
- caffeine or energy-drink use if relevant
- any recent thyroid blood-test results you have available
Also mention if you recently changed how you take levothyroxine in relation to food, medicines or supplements. Several products can change levothyroxine absorption, so consistency and a complete medication history can be important when a clinician reviews your thyroid results.
Your doctor may decide that thyroid-stimulating hormone (TSH) and thyroid hormone levels need to be checked. Symptoms alone cannot reliably show whether your thyroid hormone level is too high, too low or within the intended range.
For more information about medicine-related symptoms generally, visit our Chronic Medication Side Effects hub.
What not to do without medical advice
Do not stop thyroid medicine suddenly because you feel anxious
If you take prescription thyroid hormone, continue taking it as prescribed unless a healthcare professional tells you otherwise. NHS guidance specifically advises people experiencing levothyroxine side effects to keep taking the medicine unless advised to stop.
Stopping treatment or skipping doses can create a different thyroid hormone imbalance.
Do not lower or increase your dose yourself
The correct thyroid medicine dose depends on factors such as your thyroid condition, blood-test results, age, other health conditions and the reason treatment was prescribed.
Anxiety is useful information for your clinician, but it is not enough on its own to determine what your dose should be.
Do not take extra doses to compensate for symptoms
If you think you have missed a dose, taken an extra dose or made a dosing mistake, follow the instructions provided with your medicine or contact a pharmacist or doctor for individual advice.
Taking too much thyroid hormone can cause anxiety, nervousness, tremor, insomnia, palpitations and, in more severe cases, serious heart or neurological symptoms.
Do not assume every anxiety symptom is thyroid-related
Anxiety can have many causes. New anxiety may occur independently of thyroid disease or medicine use, and symptoms such as palpitations can also have causes unrelated to the thyroid.
Speak to a healthcare professional if anxiety is persistent, worsening, disrupting sleep or daily activities, or accompanied by other new symptoms.
Related side-effect guides and reporting options in South Africa
If you are trying to understand whether another symptom could be medicine-related, browse the side effect symptoms A-Z or our broader guide to medication side effects.
You can also discuss a suspected side effect with your doctor or pharmacist. In South Africa, suspected adverse reactions can be reported to the South African Health Products Regulatory Authority (SAHPRA). SAHPRA provides pharmacovigilance reporting routes, including the Med Safety App for patients and healthcare professionals.
Learn more about how to report side effects in South Africa.
Frequently asked questions
Is anxiety a common side effect of thyroid medicine?
It can be. NHS guidance lists feeling anxious among the common side effects of levothyroxine and notes that many side effects occur when the dose is higher than needed. Anxiety is also a symptom of hyperthyroidism itself, so a healthcare professional may need to consider both the medicine and your thyroid condition.
How long can anxiety from thyroid medicine last?
There is no single timeframe that applies to everyone. It depends on the cause. Anxiety related to excessive thyroid hormone activity may persist while thyroid hormone levels are outside their intended range, while anxiety from another cause may follow a completely different pattern.
If symptoms do not settle, are worsening or interfere with daily life, speak to your doctor or pharmacist rather than waiting indefinitely.
Should I stop my thyroid medicine if it is making me anxious?
Do not stop or change prescription thyroid medicine without professional guidance. Contact the doctor or pharmacist managing your treatment and explain when the anxiety began and whether you have other symptoms such as palpitations, tremor, sweating or insomnia.
When should I seek help?
Contact a doctor or pharmacist if anxiety is persistent, troublesome, worsening or accompanied by other signs of excessive thyroid hormone activity.
Seek urgent medical care for severe symptoms such as chest pain, fainting, severe breathing difficulty, a dangerous-feeling rapid or irregular heartbeat, seizures, severe confusion or signs of a serious allergic reaction.
Medical disclaimer: This information is for general education and does not diagnose a medical condition or replace advice from a doctor or pharmacist. Do not start, stop or change the dose of prescription thyroid medicine without professional guidance. Seek urgent medical care for severe or rapidly worsening symptoms.