Nothing is 100% safe. The word "safe" is used by almost everyone to mean a feeling they get. Something is safe to them if it feels safe. Flying is "safe" if you don't fear flying. It is not if one is afraid of getting on an airplane. Is driving a car "safe"? It is if you don't feel scared when driving in a car. Any other use of the word would need to have some statistical evaluation of the situation. Saying the risks of the treatment are outweighed by the benefit is a great rational way of saying drug is safe enough to use, but most people don't use the word safe in that way.

To me a chainsaw is a safe tool to use. Dangerous, but safe. To others it is not. Is a chainsaw a "safe" tool?