Effects of hyperthyroidism

The thyroid makes hormones that influence how quickly many body systems work. When hormone levels are too high, the heart may beat forcefully or quickly, and you may notice palpitations, tiredness or reduced exercise tolerance. The body may produce more heat, leading to excessive sweating or difficulty coping with warm surroundings. The digestive system can become more active, sometimes causing frequent bowel movements or diarrhoea.

The nervous system may feel overstimulated. Feeling anxious, irritability, trembling and difficulty sleeping can occur even when you feel exhausted. Some people develop muscle weakness or lose weight without intending to. Symptoms can build gradually, and not everyone experiences the same combination. The condition and its effects are explained further in [Hyperthyroidism](/conditions/hyperthyroidism/).

Arrange a medical assessment if these changes are new, persistent or interfering with daily activities. A clinician may ask about your symptoms, examine your neck and check your pulse, then arrange thyroid blood tests. Keep a brief record of heartbeat changes, bowel symptoms, sweating, sleep and weight changes; this can make the pattern easier to describe.

Take prescribed thyroid treatment exactly as directed and attend planned blood-test reviews, because the dose may need adjustment as hormone levels change. Do not start iodine supplements or stop treatment without medical advice. Limit triggers that make palpitations or anxiety worse, such as excess caffeine, and drink enough fluid if sweating or diarrhoea is ongoing. You can read more about [Palpitations](/symptoms/palpitations/) and [Heat Intolerance](/symptoms/heat-intolerance/).

Seek urgent medical help for chest pain, fainting, severe breathlessness, confusion, a very fast or irregular heartbeat, or a high temperature with marked agitation or weakness. These symptoms can signal a serious strain on the heart or a severe worsening of excess thyroid hormone and should not be managed at home.

Contact a clinician promptly if diarrhoea causes signs of dehydration, if weakness is worsening, or if sweating and a racing heartbeat continue at rest. For related symptom information, see [Diarrhoea](/symptoms/diarrhoea/) and [Excessive Sweating](/symptoms/excessive-sweating/).

Ask which thyroid tests you need, what may be causing the overactivity, and how soon your results should be reviewed. You can also ask which symptoms should improve first, what to do if you miss a dose, and whether any medicines or supplements you take could affect your thyroid or heart rate. Mention pregnancy, plans for pregnancy and any heart condition when discussing treatment.