In 1986, Greg Fahy read a paper about rats that were injected with cells that secreted growth hormones. The researchers did this because as rats aged, there's thymus shrinks. Because the thymus is involved in the immune system when it shrinks, rats are less able to fight off diseases so they get sick. But it turns out that injecting them with growth hormones reverses the shrinking and now the rats where more able fight off diseases. 

This is important because in humans, the thymus gland also shrinks with age, which decreases our immune system function. And this is partially why elderly people get the flu, at a higher rate. So years after reading this rat study in 2003, Greg decided to inject himself with human growth hormones and DHEA (dehydroepiandrosterone) and over one month, his thymus increased in size. After this success, he started a company named 'Intervene Immune' and injected nine volunteers with growth hormone, DHEA and Metformin and also found that their thymus increased. The most interesting part is that they also found that that volunteers Epigenetic age decreased by up to two years meaning that these people became genetically younger. Now they are doing a larger trial which should be done soon. This is really exciting because since these drugs are so cheap, this could be the first commercial drug to start reversing ageing.