What is thyroid hormone misuse?

In one line

Thyroid hormone misuse is taking a medicine meant for people whose thyroid makes too little hormone, without a prescription or in excess, to lose weight.

What is thyroid hormone misuse?
A medicine talked about as a diet pill
Among people trying to lose body fat fast, thyroid hormone pills come up. They are actually a medicine for people whose bodies do not make enough thyroid hormone. So what is thyroid hormone misuse, and what happens in the body?
In short
Using a medicine for weight loss without a prescription
Thyroid hormone misuse is taking thyroid hormone pills without a prescription, or in excess, to lose weight or body fat. 'Misuse' means using a drug wrongly or too much. As a result, the body ends up with too much thyroid hormone.
What is the thyroid?
A butterfly-shaped gland in the front of the neck
The thyroid is a small, butterfly-shaped gland in the front of the neck. It makes 'thyroid hormones' and releases them into the blood. A hormone is a substance made in one part of the body that travels in the blood and carries a signal to another part.
What are thyroid hormones?
They set how fast the body uses energy
The way the body turns food into energy and uses it is called 'metabolism'. Thyroid hormones set the speed of metabolism, which decides how much energy the body burns even at rest.
The body's control system
When levels rise, the brain sends less of its wake-up signal
A small gland under the brain called the 'pituitary' sends a hormone called 'TSH' that tells the thyroid to release its hormones. When thyroid hormone in the blood rises, the pituitary cuts back on TSH. So when thyroid hormone pills raise the level in the blood, the TSH signal that wakes up the thyroid goes down. Then the thyroid itself releases less hormone.
Use as a medicine
A pill that tops up missing thyroid hormone
When the thyroid cannot make enough hormone, the condition is called 'hypothyroidism'. People tire easily, gain weight and feel the cold a lot. In this case, a doctor prescribes thyroid hormone pills to make up for what the body cannot produce.
Why people misuse it
To speed up metabolism and lose fat
Because more thyroid hormone speeds up metabolism, people who want to lose body fat fast take it without a prescription. Among people preparing for bodybuilding contests, it is used to hit a competition weight and to lose fat first. It is usually taken in secret.
The warning on the label
The very top says it is not for weight loss
At the very top of the US label for thyroid hormone pills is a warning that they are not for weight loss. In people whose thyroid works normally, the amount the body needs does not cause weight loss. It also says larger amounts cause serious, life-threatening harm, and that this is even more dangerous with stimulants used to curb appetite.
Too much
'Hyperthyroidism': the body's functions speed up
Having more thyroid hormone than the body needs is called 'hyperthyroidism', and taking too much thyroid medicine can also cause it. People lose weight even while eating a lot, the heart beats fast or irregularly, the hands shake, they sweat a lot and cannot stand heat.
Heart and bones
The heartbeat goes off rhythm and bones weaken
Too much thyroid hormone makes the heart beat irregularly, which can lead to blood clots, strokes and a weaker heart. The drug label even lists blocked blood vessels to the heart muscle and the heart stopping. It also weakens bones, causing 'osteoporosis', where bones break easily.
Common misconception
Does thyroid hormone burn only fat?
No. When there is too much thyroid hormone, it does not pick out fat to burn; muscle shrinks too. People with a disease that makes too much thyroid hormone lost weight even while eating a lot, and most of the weight they lost was lean mass (muscle and everything except fat). When treatment brought their hormone back to normal, that weight came back.
Summary
Misusing a medicine for weight loss
Thyroid hormone misuse is taking a medicine meant for people with too little thyroid hormone, without a prescription or in excess, to lose weight. Thyroid hormone does not burn only fat; it also shrinks muscle. Related terms: metabolism, hyperthyroidism, ephedrine.