Satan is the king of this world. The medical establishment is part of this world.
So how would he use medicine for evil?
1. charmed medical equipment & supplies in hospitals
2. witches as anaesthesiologists
3. promote occult practices as legitimate medicine
4. add poisons to medicines
5. render people unhealthy and therefore dependent on the medical establishment.
6. suspend doctors' licenses who work against the above.
The above are things I have seen or heard happening.
The following shows that medicine can indeed go bad.