The thyroid is a small butterfly-shaped gland in the front of your neck, just under your voice box. It’s part of the endocrine system, which makes hormones that control the cells and organs in your body.
The main hormones the thyroid makes are triiodothyronine (T3) and thyroxine (T4). These hormones help control your growth and development. They also control the speed your body works at (your metabolism).
If your thyroid makes too much of these hormones, your body cells work faster than normal. This can make you feel irritable and nervy. You might also sweat more than usual, have diarrhoea or lose weight even though you’re eating the same amount. If your thyroid doesn’t make enough hormones, your body cells work slower than normal. This can make you feel tired and slow.
