Assuming you're fine with (somewhat debatable) casual language, "this drug (probably) causes probabilistic physical events leading to a lower chance of medically determined necessity to amputate, conditional on the correct medical examination being done at the right times".

This is analogous to how much medical research is done. Unless you want to go the literal Nazi method of inducing illness or incapacity and then testing remedies, this is sort of the best we have. Final stage medical research involves humans to test on. Preferably voluntarily, and preferably when they require the treatment through actual misfortune .