Hyperthyroidism — Overactive Thyroid Symptoms and Treatment

What Is the Thyroid Gland?

The thyroid gland is a butterfly-shaped endocrine gland normally located in the lower front of the neck. Its job is to make thyroid hormones, which are secreted into the blood and then carried to every tissue in the body. Thyroid hormones help the body use energy, stay warm, and keep the brain, heart, muscles and other organs working as they should.

The main hormones the thyroid makes are triiodothyronine (T3) and thyroxine (T4).

What Is Hyperthyroidism?

An overactive thyroid, also known as hyperthyroidism or thyrotoxicosis, is where the thyroid gland produces too much thyroid hormone.

Having too much of these hormones can cause unpleasant and potentially serious problems that may need treatment. In effect the body's metabolic engine runs permanently too fast — burning through energy reserves, driving the heart harder, and keeping the nervous system in a state of constant arousal.

It is, in almost every respect, the mirror image of hypothyroidism.

What Causes Hyperthyroidism?

Graves' disease

Graves' disease is an autoimmune condition where the immune system mistakenly attacks the thyroid, causing it to become overactive. It mostly affects young or middle-aged women and often runs in families. It is the most common cause of hyperthyroidism.

Graves' disease is also the form that can affect the eyes, producing swelling, redness, grittiness, light sensitivity, bulging of the eyeballs and occasionally double vision.

Thyroid nodules

Rarely, the thyroid can become overactive if nodules develop on the gland. Nodules are usually non-cancerous (benign), but they may contain thyroid tissue which can result in the production of excess thyroid hormones. Any nodule found during assessment follows the standard thyroid nodule evaluation pathway.

Medicines and iodine

Iodine is a mineral that the thyroid uses to create thyroid hormone. If someone is at risk for hyperthyroidism and consumes too much iodine — through diet or medications — it can cause the thyroid to produce more thyroid hormone.

Amiodarone, a medicine used to treat irregular heartbeat, contains a large amount of iodine and can cause hyperthyroidism.

Thyroiditis

Thyroiditis is inflammation of the thyroid gland, which can cause extra thyroid hormones to be released into the blood. This form is often temporary — the gland leaks its stored hormone over a few weeks or months, and function then returns to normal, sometimes passing through a period of underactivity first.

Signs and Symptoms

Common signs of hyperthyroidism include:

• Nervousness, anxiety or crankiness
• Mood swings
• Fatigue or weakness
• Sensitivity to heat
• A swollen thyroid — called a goitre
• Losing weight suddenly, without trying
• Fast or uneven heartbeat, or palpitations — a pounding sensation in the chest
• Having more bowel movements
• Shaking of the hands and fingers — tremor
• Sleep problems
• Thinning skin
• Fine, brittle hair
• Changes in the menstrual cycle

The cardiovascular symptoms deserve emphasis. A resting heart rate persistently above 100, or an irregular rhythm, is not something to monitor at home — particularly in older adults, where hyperthyroidism can trigger atrial fibrillation and carries a genuine risk of stroke.

Where a goitre is large, it can also press on the windpipe and oesophagus, causing a sensation of tightness, a persistent cough, or difficulty swallowing.

How Hyperthyroidism Is Diagnosed

Physical examination

• Thyroid gland examination — gently feeling the thyroid gland through the outside of the neck to check if it is enlarged, bumpy or tender.
• Eye examination — checking for swelling, redness, bulging and other signs of Graves' eye disease.
• Heart rate — examining for an irregular rhythm or a rapid heart rate.
• Hands — examining for tremor or changes in the colour of the fingernails.
• Skin — examining for characteristic warmth and moistness.

Blood tests

In hyperthyroidism, levels of the thyroid hormones T3 and T4 are above normal, and thyroid-stimulating hormone (TSH) is lower than normal.

The reason TSH falls is the same feedback loop that raises it in hypothyroidism, running in reverse: sensing excess circulating hormone, the pituitary shuts down its own output. A suppressed TSH is therefore usually the first abnormal result to appear.

Imaging tests

Radioactive iodine uptake (RAIU) test. A small amount of radioactive iodine is swallowed, then a device called a gamma probe measures how much of the iodine collects in the thyroid gland. If this uptake is high, the patient probably has Graves' disease or thyroid nodules. Low uptake instead suggests thyroiditis, where the gland is leaking stored hormone rather than overproducing it — an important distinction, because thyroiditis does not respond to the same treatments.

Ultrasound. Uses sound waves to create images of the thyroid gland, assessing its size, texture and any nodules.

How Hyperthyroidism Is Treated

There are three definitive approaches, and the right one depends on the cause, the severity, the patient's age and their circumstances.

Antithyroid drugs

Methimazole or propylthiouracil block the ability of the thyroid to make hormones.

These are frequently the first step, particularly in Graves' disease, and are typically continued for 12–18 months before an attempt is made to withdraw them. Remission is possible, though relapse is common.

Regular blood monitoring is essential — both to keep the dose correct and to watch for uncommon but serious side effects including a severe fall in white cell count and liver toxicity. Beta-blockers are often prescribed alongside to control palpitations, tremor and anxiety while the antithyroid drug takes effect.

Propylthiouracil is generally reserved for specific situations such as the first trimester of pregnancy.

Radioactive iodine

Radioactive iodine (RAI), also called radioiodine, effectively destroys the cells that produce thyroid hormones without damaging other bodily tissues. It is usually taken as an oral tablet or liquid.

It works because the thyroid is the only organ that actively concentrates iodine, so the radiation is delivered almost entirely where it is needed. The expected long-term outcome is permanent hypothyroidism, which is then managed straightforwardly with daily thyroxine.

Our full guide covers radioactive iodine therapy — preparation, procedure and the radiation safety rules afterwards.

Surgery — thyroidectomy

Thyroidectomy is a surgery in which the whole or part of the thyroid gland is removed.

Surgery is preferred where there is a large compressive goitre causing breathing or swallowing difficulty, a suspicious or confirmed malignant nodule, severe Graves' eye disease that radioactive iodine might worsen, intolerance of antithyroid drugs, or a wish to conceive in the near future.

The principal surgical considerations are the recurrent laryngeal nerves, which run immediately behind the gland and control the vocal cords, and the four parathyroid glands that regulate calcium. Injury to the former can cause vocal cord paralysis and voice change; damage to the latter causes low calcium. Both are the reason thyroid surgery belongs with surgeons who do it regularly. Recovery is covered in thyroidectomy — types, recovery and life after surgery.

Hyperthyroidism and Hypothyroidism Compared

It is worth knowing that both radioactive iodine and total thyroidectomy deliberately produce hypothyroidism. This is not a failure of treatment — it is the intended endpoint, because a predictable underactive thyroid managed with a daily tablet is considerably safer than an uncontrolled overactive one.

Thyroid Care at THANC

Thyroid conditions at THANC are managed through the thyroid and parathyroid surgery service.

Our surgical practice focuses on preserving the structures that determine quality of life after thyroid surgery — the recurrent laryngeal nerves that control the voice, and the parathyroid glands that regulate calcium. Because voice outcomes matter as much as the operation itself, patients with voice change before or after surgery are assessed jointly with our laryngology service.

Where a second view on a thyroid mass would help, we offer a thyroid and parotid tumour second opinion.

Book a consultation to discuss symptoms of an overactive thyroid or a neck swelling.