Why it happens
The most common cause is autoimmune (Hashimoto) thyroiditis. Others include iodine deficiency, thyroid surgery or radioiodine treatment, some medicines such as lithium or amiodarone, and being born with a poorly working thyroid. It is more common in women.
Symptoms
- Tiredness and feeling cold
- Weight gain and constipation
- Dry skin and thinning hair
- Low mood, slowed thinking, muscle aches
- Heavy or irregular periods
These are common in many conditions, so the diagnosis rests on blood tests, not symptoms alone.
Diagnosis
A raised TSH with a low free T4 confirms an underactive thyroid. A raised TSH with a normal T4 is called subclinical hypothyroidism, and treatment depends on the level, symptoms, antibodies and whether you are pregnant.
Treatment
Levothyroxine replaces the missing hormone, usually for life. It works best taken on an empty stomach, commonly in the morning, 30 to 60 minutes before breakfast, and at least four hours apart from calcium or iron tablets. Your dose is adjusted by blood tests, with TSH checked about 6 to 8 weeks after a change and then about once a year when stable.
- Do not stop the tablet when you feel well.
- Tell your doctor if you become pregnant; the dose often needs adjusting early.
- Treatment corrects part of the weight gain but is not a weight-loss treatment.
When to see a specialist
Consider an opinion if you still feel unwell on treatment, your TSH is hard to control, you are pregnant or planning pregnancy, or your child has a thyroid problem.
This guide is general information and is not a substitute for a consultation.