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Underactive Thyroid (Hypothyroidism): Symptoms, Tests and Treatment
Tiredness, weight gain and feeling cold can be signs of an underactive thyroid. Learn how hypothyroidism is diagnosed with a blood test and treated.
Quick answer
An underactive thyroid (hypothyroidism) means the thyroid gland makes too little hormone, causing tiredness, weight gain, feeling cold, constipation, dry skin and low mood. It is diagnosed with a blood test for TSH and thyroxine (T4) and is usually treated with a daily levothyroxine tablet, with regular blood tests to adjust the dose.
The thyroid is a small gland in the neck that controls how fast the body uses energy. When it is underactive, many body processes slow down.
Symptoms
Symptoms develop slowly and can be mistaken for stress or ageing:
- Tiredness and sluggishness
- Weight gain
- Feeling cold
- Constipation
- Dry skin and hair, hair thinning
- Low mood
- Heavy or irregular periods
- Muscle aches
Who is at risk?
Hypothyroidism is more common in women and with increasing age. The risk is higher if you have a family history of thyroid disease, another autoimmune condition such as type 1 diabetes, or have had thyroid surgery or radioactive iodine treatment.
How it is diagnosed
A blood test measures:
- TSH (thyroid-stimulating hormone): high in an underactive thyroid
- Free T4 (thyroxine): low or low-normal
Your GP will interpret the results with your symptoms. Sometimes the test is repeated before starting treatment.
Treatment
The usual treatment is levothyroxine, a tablet that replaces the missing hormone.
- Take it at the same time each day, usually in the morning on an empty stomach with water.
- Avoid taking it at the same time as iron or calcium supplements, which reduce absorption.
- Blood tests are repeated after dose changes until the level is right, then usually once a year.
Most people need treatment for life, and feel much better once the dose is correct.
Pregnancy
Thyroid hormone is important for a baby's development. If you have hypothyroidism and are planning pregnancy or become pregnant, tell your doctor promptly, as your dose often needs adjusting.
When to see a doctor
Book a GP visit if you have several of the symptoms above for weeks, or a swelling in your neck.
Frequently asked questions
Can I stop levothyroxine when I feel better?
No. Feeling better means the dose is working. Stopping it usually brings symptoms back.
Does diet cure an underactive thyroid?
No diet cures hypothyroidism. A balanced diet supports general health, but the hormone needs to be replaced with medicine.