Hypothyroidism (underactive thyroid)

Your thyroid is a small gland in your neck. It makes hormones that control how fast your body uses energy. If you have an underactive thyroid (hypothyroidism), it does not make enough of these hormones, so many of your body's processes slow down.

It is common. In the UK it affects about 15 in every 1,000 women and 1 in every 1,000 men. It is most common in women over 60.

Symptoms

Symptoms usually come on slowly, over months or years, and can be easy to mistake for other things:

• tiredness and feeling slow
• weight gain
• feeling cold
• constipation
• dry skin and thinning hair
• aches and pains, muscle cramps
• low mood or depression
• poor memory and concentration
• heavy or irregular periods
• a slow heart rate

Causes

• autoimmune thyroid disease (Hashimoto's), where the immune system attacks the thyroid. This is the most common cause in the UK
• treatment for an overactive thyroid, such as radioactive iodine or surgery
• some medicines, such as lithium or amiodarone
• radiotherapy to the neck
• rarely, a problem with the pituitary gland in the brain

Getting diagnosed

A simple blood test checks your levels of TSH (thyroid stimulating hormone) and thyroxine (T4). A high TSH and low T4 usually means an underactive thyroid. Sometimes the test is repeated to be sure.

Some people have a slightly raised TSH with normal T4. This is called subclinical hypothyroidism. It does not always need treatment, but your GP may check it again.

Treatment

Most people take a daily tablet called levothyroxine. See hypothyroidism treatment.