Can excess iodine cause hyperthyroidism?

Iodine is used to make thyroid hormones. A sudden or unusually high iodine exposure can disturb hormone production in some people and may lead to an overactive thyroid. Sources can include supplements, some medicines, seaweed products, or iodine-containing contrast used for certain scans. The effect depends on the source, amount, previous thyroid health, and other factors. Symptoms of hyperthyroidism may include a fast or pounding heartbeat, feeling anxious, difficulty sleeping, excessive sweating, heat intolerance, diarrhoea, or night sweats. These symptoms can have other explanations, so they do not confirm the cause.

Tell a clinician about every supplement, medicine, seaweed product, and recent scan before changing anything. Do not start iodine supplements to treat thyroid symptoms unless prescribed. A clinician can check your symptoms, pulse, neck, and thyroid blood tests, then decide whether further tests are needed. Keep the product packaging or a photograph of its label if possible. Follow any instructions given after a contrast scan and mention known thyroid disease.

Arrange prompt medical review for new palpitations, persistent sweating, unexplained weight change, shaking, diarrhoea, or marked restlessness after an iodine exposure. Seek emergency help for chest pain, fainting, severe breathlessness, confusion, or a very rapid or irregular heartbeat. Untreated hyperthyroidism can place strain on the heart and other systems, so worsening symptoms should not wait for a routine appointment.

Could iodine from my supplement, medicine, food, or scan be contributing? Which thyroid tests are appropriate? Should I stop or replace a product, and which symptoms require urgent help?