Hyperthyroidism means the thyroid gland produces more hormone than the body needs. Because thyroid hormone sets the pace of metabolism, an excess speeds many body systems up — sometimes subtly, sometimes dramatically.
What hyperthyroidism does
Thyroid hormone influences heart rate, temperature regulation, digestion, mood and energy use. When levels are high, the body runs fast: the heart races, weight falls despite a normal appetite, and the person feels hot, restless and anxious.
It is the opposite picture to hypothyroidism, though some symptoms — such as fatigue — overlap.
Common causes
Several conditions cause an overactive thyroid, and identifying the cause matters because treatment differs:
- Graves’ disease — an autoimmune condition that stimulates the thyroid; the most common cause.
- Toxic nodular disease — one or more nodules that produce hormone independently.
- Thyroiditis — inflammation that leaks stored hormone (often temporary).
- Excess iodine or medication — including amiodarone and some contrast dyes.
Symptoms to recognise
Typical features include:
- Palpitations, a fast or irregular heartbeat
- Unexplained weight loss with a normal or increased appetite
- Heat intolerance and excessive sweating
- Tremor, anxiety, irritability and difficulty sleeping
- Frequent bowel movements
- Fatigue and muscle weakness
- In Graves’ disease, eye changes such as bulging or grittiness
Older adults may present differently — sometimes with an irregular heartbeat or weight loss rather than the classic picture.
How it is diagnosed
Diagnosis starts with blood tests. A low TSH with high free T4 (and often high free T3) confirms an overactive thyroid. The next step is finding the cause: antibody tests such as TRAb point to Graves’ disease, while a thyroid scan or uptake test helps distinguish Graves’ from thyroiditis.
An ultrasound may be used to assess nodules.
Treatment options
There are three main treatments, and the best choice depends on the cause, your age, the size of the gland, whether you have eye disease, and your preferences.
Antithyroid medication
Drugs such as carbimazole or methimazole reduce hormone production. They are often used first, especially in Graves’ disease, and a course may last 12–18 months. Regular blood tests monitor thyroid function and, rarely, side effects. Propylthiouracil is preferred in the first trimester of pregnancy.
Radioactive iodine
Radioactive iodine is taken as a capsule or drink and is concentrated by the thyroid, gradually reducing its activity. It is convenient and effective but usually leads to an underactive thyroid, which is then treated with levothyroxine. It is avoided in active eye disease and in pregnancy.
Surgery
Removing part or all of the thyroid is an option for a large goitre, for nodular disease, or when other treatments are unsuitable. It requires an experienced surgeon and lifelong monitoring afterwards.
Beta-blockers are often used alongside these treatments to control symptoms such as palpitations and tremor while the underlying problem is addressed.
Why treatment matters
Untreated hyperthyroidism can cause atrial fibrillation, heart failure, thinning of the bones and, rarely, a dangerous surge of symptoms called thyroid storm. It also affects fertility and pregnancy. Prompt treatment brings symptoms under control and prevents complications.
Living with an overactive thyroid
With treatment, most people feel better within weeks, though full control can take longer. Regular monitoring is essential, and after radioactive iodine or surgery, lifelong thyroid hormone replacement is usually needed — a straightforward trade for stable health.
If you have symptoms of an overactive thyroid, seek assessment rather than waiting. The condition is very treatable once identified.