Scientist doping

I am currently sitting in on an ethics class because NIH requires that I do so if I want to accept their funding. I had an ethics class as a graduate student and we talked about all of the usual things like stem cell research, gene therapy, experimentation with animals, etc. The ethics class I am in now is a bit different, which is nice because I can think about some new issues. The issue up for discussion yesterday was sports doping, which is when athletes take drugs to enhance their natural abilities. Most people find this unethical because athletes should perform using only what is available to them naturally. Enhancement is considered to be unfair and a sign of bad sportsmanship. But I couldn't help but compare the enhancement of athleticism using steroids to the enhancement of brain power/alertness using caffeine. Every day I enhance my alertness by drinking tea or coffee. Does this mean that I have an unfair advantage in science because I am doping my brain with caffeine? I would say no but only because the majority of scientists I know rely on caffeine themselves. Basically, we are all enhancing our natural abilities. But no one has a problem with this. So I guess caffeine enhancement of scientists is not as unethical as steroid enhancement of athletes. Why is this?