How replacement Thyroxine came about
You might be surprised to know that the history of thyroid hormone replacement goes back over a hundred years ago when the first thyroid extracts were obtained from sheep thyroid glands and injected into humans.
These were the first recorded treatments of what they called “myxedema” and what we refer to as thyroid failure.
Over the years, the animal products became refined and were created as desiccated - or dried products.
Then, in the 1960’s the hormone Thyroxine was identified as a molecule and was therefore able to be chemically recreated. This means we are now able to manufacture the human version of thyroid hormone –medically described as T4.
Thyroxine now constitutes the standard replacement preparation - indeed figures from 2007 shows Thyroxine being prescribed to 3% of the English population. This is because it is produced such that it is chemically indistinguishable from that which your thyroid would naturally be producing.
In terms of checks and balances in the body, we rely on the pituitary gland telling us when thyroid hormone levels are adequate. Astonishingly, this is the case even when a patient may have lost their thyroid gland - their pituitary gland will still be talking to their thyroid as it was there and telling us when we have the correct amount of thyroid hormone back in the system!
Because of this pituitary feedback, we are supplied with a certain target to aim for in terms of TSH or - thyroid stimulating hormone – thus reproducing what we think you would have been like in normal health.
For 95% of patients getting the right dose is relatively straightforward but since Thyroxine therapy is almost always life-long, it’s important to continually monitor. This avoids the danger of taking too much which can be the cause of developing abnormal heart rhythms (thus increasing the risk of stroke) or losing bone - particularly in post-menopausal women - which may increase your risk of osteoporosis.