By Michelle Roberts
BBC News health reporter
It is difficult to imagine a world without hormones.
JFK had Addison's disease
Had they not been discovered 100 years ago, John F Kennedy would have lost his life as a young man to a hormonal imbalance, rather than to a bullet as US President.
People with Type 1 diabetes would still die because there would be no insulin therapy to treat them.
There would be no oral contraceptive pills and no babies born by IVF.
A century of discovery
It was Ernest Henry Starling who first coined the term 'hormone' in 1905.
He had been dining with academics at Cambridge University and needed a word to describe an agent released into the bloodstream that caused activity in a different part of the body.
It is thought that a colleague who was an authority on Greek poetry suggested the Greek verb for 'excite' or 'arouse', and the deed was done.
Scientists had been aware of such chemicals earlier than this.
In 1855, Thomas Addison described and later gave his name to the syndrome that would have killed JFK.
But he was largely ignored, and when the London Medico-Chirurgical Society would not publish his findings he committed suicide.
A French doctor called Brown-Sequard believed extract of testicles had a rejuvenating effect in man and tested it on himself.
Similarly, George Oliver, a spa physician working in Harrogate in 1893, believed extracts of the adrenal glands might raise low blood pressure and used his son as a guinea-pig.
1132 - Hsu Shu Wei prescribes pig's testicular extract for impotence
1855 - Thomas Addison describes what became known as Addison's disease
1912 - Schaefer names "insulin"
1950 Hench and Kendall treated rheumatoid arthritis with cortisone
1978 - Louise Joy Brown, the first test tube baby, is born thanks to the discovery of sex hormones
Since then, more than 30 different hormones have been discovered and have changed the course of medicine and, in particular, the drugs we take.
Professor Ashley Grossman, consultant endocrinologist at Barts and the London Hospital, said: "The most dramatic discovery was insulin.
"Years ago, if you developed Type 1 diabetes then within a few weeks you were dead.
"But the earliest of all of the hormone diseases to be diagnosed was Addison's disease, which was lethal until it was discovered that it was down to the adrenal glands not making cortisone.
"They started giving steroids to these patients and they lived."
But there is a darker side to some of the discoveries.
In the 1950s and 60s, thousands of children born with a condition that means they never reach adult height were given injections of extracts of human pituitary glands from dead bodies.
"We now know that some of those bodies had the human form of mad cow disease, CJD, so a small but significant percentage of those children died," said Professor Grossman.
He said taking steroid medicines over a long period of time, for arthritis for example, could give unwanted side effects.
He said it was possible to develop a condition similar to Cushing's syndrome, which is caused by too much of the hormone cortisol in the body.
This can cause a multitude of problems such as unwanted weight gain, diabetes and osteoporosis.
Since sex hormones like testosterone were found, athletes have abused these steroids to out-perform opponents.
The animals we eat are also fed hormones to make them plumper and meatier.
Future fat fighter
Some fear female sex hormones are entering our water supplies via the urine of the millions of women using the contraceptive pill around the world.
They say this is changing the sex of male fish and potentially hampering human fertility.
Professor Grossman said most of the hormone research going on now was to look for ways to fight obesity.
Two have already been found - leptin, which tells your brain that it is full, and ghrelin, the hunger hormone that tells you to eat.
"Once we work out how they work we can block them and allow people to control their body shape," he said.
"I'm sure we will continue to see dramatic discoveries. There are still quite a few hormones out there that we have yet to find."