In which competitions is it fair to use performance enhancing drugs?

Is it ok to take beta blockers as a musician to quiet your anxiety so you can perform well in music competitions that win you prestigious prizes?

Is it ok to take steroids that enhance your strength in competitions where strength is crucial?

Is it ok to sleep in an oxygen depleted tent in order to simulate high altitude training?

Is it ok to take drugs that enhance the capability of your blood to hold onto oxygen, as if you have been training at high altitude?

Is it ok to take steroids in order to bulk up and do well as a laborer in a high paying dock worker job?

Is it ok to take the drug cocktails that students take these days in order to do better on tests (assume the drugs work)?

There are many situations where people take drugs in order to do better. In some competitive professions, it is against the rules. In others, there are no rules against the drugs.

Is there any reasonable principle that would help us figure out when drugs should be illegal and when they are ok? Is there any consistency here? If not, how do you explain the difference between situations where it is ok, and situations where the ruling bodies have made taking drugs illegal?