Several medicines can raise TSH, either by making the thyroid produce less hormone or by reducing how much thyroid replacement medicine the body absorbs. Examples include lithium and amiodarone. Some cancer treatments and medicines used to treat an overactive thyroid can also lead to higher TSH. Calcium, iron, and certain stomach or cholesterol medicines may raise TSH in people taking levothyroxine.
How can medicines increase TSH levels?
Thyroid-stimulating hormone (TSH) is produced by the pituitary gland in the brain. It signals the thyroid gland in the neck to make thyroid hormones, which help regulate energy use and other body functions. When the body has too little thyroid hormone, the pituitary gland usually releases more TSH to encourage the thyroid to work harder.
Medicines can affect this process in different ways. Some interfere with thyroid hormone production or cause inflammation of the thyroid gland. Others reduce the absorption of levothyroxine, a medicine used to replace thyroid hormone. A higher-than-expected TSH result may therefore be related to a medication, but other causes are possible. According to MedlinePlus, TSH testing alone cannot establish the cause of an abnormal result.
Which medicines can raise TSH?
The medicines most relevant to a higher TSH result fall into several groups. Their effects depend on the drug, dose, duration of use, thyroid health, and other treatments a person takes. Some medicines can cause an underactive thyroid, while others mainly affect thyroid test results or the effectiveness of thyroid replacement treatment.
- Lithium: A medicine used to treat bipolar disorder and certain other mood conditions. It can interfere with thyroid function and contribute to an underactive thyroid.
- Amiodarone: A medicine used to treat certain abnormal heart rhythms. Its high iodine content and effects on the thyroid can lead to either an underactive or overactive thyroid.
- Antithyroid medicines: Medicines such as methimazole, carbimazole, and propylthiouracil reduce thyroid hormone production. If their effect is greater than needed, thyroid hormone levels may fall and TSH may rise.
- Some cancer treatments: Certain targeted cancer drugs and immune-based treatments can affect thyroid function, sometimes causing thyroid inflammation or an underactive thyroid.
- Iodine-containing medicines: Large amounts of iodine, including from some iodine-containing preparations, can interfere with thyroid hormone production in susceptible people.
1. Lithium
Lithium is one of the best-established medication-related causes of thyroid dysfunction. It can affect the thyroid's ability to release hormones, and thyroid function may change during long-term treatment. If thyroid hormone production falls, TSH can increase. The effect does not occur in everyone who takes lithium.
The UK National Health Service (NHS) explains that long-term lithium treatment can cause thyroid problems and that healthcare professionals may arrange blood tests to monitor thyroid function. People taking lithium should continue their prescribed treatment unless their prescriber advises otherwise, even when a thyroid test is abnormal.
2. Amiodarone
Amiodarone is used for certain heart rhythm disorders and contains a substantial amount of iodine. It can alter thyroid hormone production and may cause hypothyroidism, which can lead to higher TSH. It can also cause hyperthyroidism, in which thyroid hormone levels become too high and TSH is often low. The direction of the change depends on the type of thyroid effect.
The NHS Specialist Pharmacy Service recommends thyroid function testing before and during amiodarone treatment because thyroid changes can develop while taking the medicine. Its amiodarone monitoring guidance also explains that thyroid test changes must be interpreted alongside the person's hormone levels and clinical situation.
3. Medicines that suppress thyroid hormone production
Antithyroid medicines are prescribed to reduce excessive thyroid hormone production. Examples include methimazole, carbimazole, and propylthiouracil. These drugs are intended to bring thyroid hormone levels under control, but the amount of medication needed can change over time. If hormone production becomes lower than the body needs, TSH may rise.
Iodine-containing drugs and certain cancer treatments can also affect thyroid function through different mechanisms. The medical reference Endotext, available through the U.S. National Library of Medicine, describes several medication groups that can interfere with thyroid hormone production, metabolism, or regulation. These effects do not mean that everyone using these medicines will develop an abnormal TSH result.
Can medicines raise TSH in people taking levothyroxine?
Yes. People taking levothyroxine for an underactive thyroid may have a higher TSH result if another medicine reduces how much levothyroxine enters the bloodstream. In this situation, the second medicine may not directly damage the thyroid. Instead, the body may receive less thyroid hormone replacement than expected.
Medicines and supplements that can interfere with levothyroxine absorption include:
- Calcium supplements: These can reduce levothyroxine absorption when taken too close together.
- Iron supplements: Iron can bind to levothyroxine in the digestive tract and reduce absorption.
- Antacids and some indigestion medicines: Certain products can interfere with absorption, depending on their ingredients.
- Cholesterol-lowering medicines: Drugs such as cholestyramine and colestipol can reduce the amount of levothyroxine absorbed.
- Sucralfate and some other medicines: These may interfere with levothyroxine absorption.
- Some acid-reducing medicines: Proton pump inhibitors may affect thyroid replacement requirements in some people.
Leeds Teaching Hospitals NHS Trust explains that calcium, iron, indigestion medicines, and several other products can reduce levothyroxine absorption. The appropriate interval between doses depends on the medicine and its instructions. A pharmacist or prescriber can advise on how to space them correctly.
Taking levothyroxine inconsistently, taking it too close to food, or changing how it is taken may also affect treatment results. If TSH becomes higher after starting a new medicine or supplement, the healthcare professional reviewing the result may assess the timing of doses, adherence, and possible interactions before deciding whether the levothyroxine dose needs to change.
Can other medicines affect thyroid blood test results?
Yes. Some medicines change thyroid hormone levels, while others affect the hormones that regulate the thyroid or alter the interpretation of blood tests. These effects do not all cause high TSH. For example, glucocorticoids such as prednisone and dopamine can lower TSH in certain circumstances. This is one reason a medication list is important when reviewing an unexpected result.
Healthcare professionals may consider prescription medicines, over-the-counter products, vitamins, supplements, and recent changes in treatment. Biotin, a vitamin found in some hair and nail supplements, can interfere with certain thyroid blood tests. The effect depends on the test method, so the laboratory or healthcare professional should be told about its use before testing.
What should you do if your TSH rises after starting a medicine?
A higher TSH result after starting a medicine is useful information, but it does not automatically prove that the medicine caused the change. The next step is to review the timing of treatment and the complete thyroid test results with the healthcare professional responsible for your care.
To make that review more useful, share the following details:
- The names and doses of all prescription medicines, over-the-counter products, and supplements you take.
- When each medicine was started, stopped, or changed in dose.
- How you take levothyroxine, if prescribed, including its timing in relation to food, calcium, iron, and other medicines.
- Previous TSH results and any available free T4 results, which help show how thyroid function has changed over time.
- Any new or worsening symptoms, such as unusual tiredness, feeling unusually cold, constipation, or changes in weight.
A clinician may recommend repeat TSH testing, a free T4 blood test, or other investigations depending on the situation. The timing of repeat testing depends on the medicine involved, the pattern of results, and the reason treatment was prescribed.
Do not stop a prescribed medicine or change its dose on your own. Some medicines, including lithium and amiodarone, are used to manage important medical conditions and may require specialist review if thyroid function changes. In some cases, the prescriber can adjust treatment or manage a medication-related thyroid problem while continuing the original medicine.