Medical science progresses so slowly due to ethical concerns causing an inability to experiment on human models. Things need to be vigorously tested in a number of animal models before trials on human begin and even then the slightest side effect is enough to cause cessation of the trial.

What if we created a headless human model for experimenting on? It wouldn't be conscious and so it couldn't experience any suffering, it would be perfectly fine to experiment on. It would need to be fed through IV and have various hormones supplemented due to lack of pituary gland, but it would still be an amazing model to experiment on.

You could get a headless human in 2 ways. You could take a death row inmate and execute him by surgically removing his head whilst keeping the body alive or take a developing embryo and suppress the development of a head and brain by blocking the right differentiating factors.