Hypothyroidism: symptoms, testing and treatment

Hypothyroidism is an underactive thyroid that does not produce enough thyroid hormone for the body’s needs.

Thyroid hormone helps regulate energy use, temperature and many organ functions. Low levels can slow these processes, often causing changes that build gradually. Treatment replaces the missing hormone and is tailored using symptoms and blood-test results.

Common experiences include tiredness, feeling cold, constipation, daytime sleepiness, dry skin, slower thinking, low mood, weight gain, muscle aches or cramps, and changes in menstrual periods. Hypothyroidism often presents with cold intolerance and unexplained weight gain, but either symptom can also have other explanations.

Autoimmune thyroid disease is a common cause, where the immune system gradually damages thyroid tissue. Previous treatment for an overactive thyroid, thyroid surgery, some medicines and inflammation of the gland can also lead to low hormone levels. Less often, the problem starts in the part of the brain that controls thyroid stimulation.

Symptoms can develop slowly enough to be mistaken for stress, ageing or another condition. Once replacement treatment begins, improvement may be gradual while the dose is adjusted. Do not stop thyroid hormone suddenly unless the prescriber advises it, as low levels can return.

A family history of thyroid disease or autoimmune illness can be relevant. Risk may also be higher after pregnancy, neck radiation, thyroid surgery or treatment for hyperthyroidism. Tell the clinician about lithium, amiodarone and supplements that may contain iodine or thyroid hormone.

Diagnosis relies on blood tests that show how the thyroid and its controlling hormone are working. The clinician will ask about symptoms, review medicines and examine the neck for enlargement or nodules. Antibody testing may help identify autoimmune thyroid disease, while additional testing is chosen for unusual results.

Levothyroxine, a synthetic form of thyroid hormone, is the usual replacement treatment. It is taken consistently as directed so blood levels can be interpreted accurately. The dose is based on test results and personal factors, and it may be adjusted after follow-up testing. Some foods, supplements and medicines can affect absorption, so ask when to take them.

Keep repeat blood-test appointments and take the same product in the same way each day unless instructed otherwise. Mention pregnancy planning or pregnancy promptly because thyroid requirements may change. A symptom diary can help distinguish thyroid-related changes from sleep, mood or other health concerns.

When low thyroid hormone is not treated, symptoms may become more limiting and can affect cholesterol, heart function, fertility and pregnancy. Severe longstanding hypothyroidism can rarely lead to marked drowsiness, confusion and low body temperature, which needs urgent medical care.

Autoimmune hypothyroidism cannot usually be prevented. Avoid self-treating with iodine or thyroid supplements, as they can disrupt thyroid function. For people already taking replacement hormone, regular monitoring is the practical way to prevent levels becoming too low or too high.

A GP can arrange initial tests and ongoing monitoring. An endocrinologist may be involved when results are complex, symptoms persist despite treatment, pregnancy requires closer management, or another thyroid condition is suspected. Bring medicine and supplement details to appointments.