Hyperthyroidism and blood clots: what to know

Excess thyroid hormone can place extra strain on the cardiovascular system and may contribute to a fast or irregular heartbeat. Some people with thyroid disease also have other clot risks, such as pregnancy or recent delivery, immobility, surgery, smoking, or certain medicines. A symptom such as a swollen painful leg or sudden breathlessness is not proof of a clot, and should not be explained away as hyperthyroidism. Learn about [Hyperthyroidism](/conditions/hyperthyroidism/) and notice [Palpitations](/symptoms/palpitations/) as a separate heart symptom.

If you have diagnosed hyperthyroidism, keep follow-up appointments so thyroid levels and pulse can be reviewed. Give the clinician a complete history of previous clots, pregnancy or postpartum status, travel or immobility, operations, smoking, and hormone medicines. Do not start aspirin, anticoagulants, or supplements on your own. Treatment decisions depend on examination and testing, which may include blood tests, an ECG, or imaging when a clot is suspected.

Call emergency services for sudden breathlessness, chest pain that may worsen when breathing, coughing blood, fainting, or severe weakness. Seek urgent assessment for one-sided leg swelling, warmth, redness, or pain, particularly after immobility or delivery. A racing or irregular heartbeat with dizziness, chest discomfort, or breathlessness also needs immediate attention.

Ask: Does my thyroid level or heart rhythm need checking? Do I have personal risk factors for clots? Which symptoms should send me to emergency care? Are my contraceptive or hormone medicines relevant? If treatment changes, how will clot and bleeding concerns be balanced?