The thyroid gland produces hormones that affect your heart rate and body temperature, according to the NHS.
It’s found at the front of your neck, just below the Adam’s apple.
The gland is responsible for making two types of hormone that are secreted into the blood; thyroxine and triiodothyronine.
But, if the thyroid produces too much thyroxine for what the body actually needs, it could cause hyperthyroidism, or an overactive thyroid.
“An overactive thyroid [hyperthyroidism] can cause a wide range of possible symptoms, although it’s unlikely you’ll experience all of them,” said the NHS.
“The symptoms may develop gradually or suddenly. For some people they’re relatively mild, while for others they can be severe and significantly affect their life.
“See your GP if you have symptoms of an overactive thyroid.
“These symptoms can have a number of causes. But a simple blood test can often help determine whether they’re caused by a problem with your thyroid.”
Common symptoms of hyperthyroidism include anxiety, difficulty sleeping, diarrhoea and hyperactivity.
Patients could also feel tired all of the time and always thirsty.
The symptoms could also stretch to physical signs of the condition.
Having a swollen neck, hair loss or red palms may be signs of an overactive thyroid.
You could develop an overactive thyroid if you have Grave’s disease – where the body’s immune system mistakenly attacks the thyroid gland.
Hyperthyroidism may also be caused by developing lumps on the thyroid gland, the NHS said.
An overactive thyroid can affect anyone, but it’s about 10 times more likely to develop in women than men.
Those most at risk are people aged between 20 and 40.
