Human growth hormone is produced in the pituitary gland in the brain and is essential for childhood growth and the development of muscle, bone and cartilage.
But the older we get the less we produce, which is why it has been called the "youth" hormone. Until the 1990s, the only source was pituitary glands from cadavers but it has since become available in synthetic form, as a drug for injection.
It is prescribed to children who have stopped growing too early because they are deficient in the hormone to boost their adult height. Some Harley Street doctors also prescribe it to patients whom they deem to be deficient in the hormone.
Anecdotal reports suggest its popularity is growing among sportsmen as a substitute for anabolic steroids which are perceived to have more serious side effects. But human growth hormone has them too. It can lead to swelling of the body's soft tissues, abnormal growth of the hands, feet and face, high blood pressure, blood clots, diabetes, increased sweating, and excessive hair growth. Organs including the heart, liver and kidneys, may also grow excessively, leading to potentially life-threatening problems such as cardiomyopathy, a disease of the heart muscle. Researchers have also linked HGH to an increased risks of cancer and overloading of the adrenal glands, which can result in infection and illness.