Aspirin and hyperthyroidism: what you should know

This concern is most relevant when aspirin is taken repeatedly for pain, inflammation or fever. A clinician can distinguish that situation from low-dose aspirin prescribed to help prevent blood clots.

In the blood, much thyroid hormone is attached to carrier proteins. Aspirin can displace some hormone from those proteins, temporarily increasing the unbound portion that acts on tissues. Higher or repeated doses may therefore intensify features of hyperthyroidism such as a racing heartbeat, tremor, heat intolerance, sweating or anxiety.

Aspirin can also alter thyroid blood-test results, so tell the clinician ordering or interpreting tests when and how much you have taken. The result needs to be considered alongside symptoms, examination findings and other thyroid measurements.

Do not start aspirin for fever, pain or inflammation without checking with a doctor or pharmacist who knows about your thyroid condition. Give them the product name, dose, reason for use and every other medicine or supplement you take. Some cold and pain products contain aspirin even when the front label emphasises another ingredient.

If aspirin was prescribed for your heart, circulation or another diagnosed problem, do not stop it on your own. Contact the prescriber to review whether it should continue and what monitoring is appropriate. Your clinician can also advise on a suitable alternative for pain or fever based on your liver, kidney, stomach and other health conditions.

Get urgent medical help for a very fast or irregular heartbeat, chest pain, fainting, severe breathlessness, marked confusion, extreme agitation, high fever, persistent vomiting or severe weakness. These signs require prompt assessment whether or not aspirin caused them.

Seek emergency care after aspirin if you develop swelling of the lips or tongue, trouble breathing, vomit containing blood, black stools, or bleeding that will not stop.

Ask whether the reason for aspirin still applies, whether your current dose could affect thyroid tests, which symptoms should trigger an urgent review, and which pain or fever medicine fits your medical history. Also confirm when thyroid blood tests should be taken in relation to recent aspirin use.