This question doesn't really make sense to me because everything is a trade-off fundamentally. If the human body could perform better without any negative side effects, then it would do so already. This is why I'm suspicious of all drugs and don't take them unless it's absolutely necessary. The only way your scenario could work is by magic, and in that case I'd rather the magic be in the form of some spell or affirmation or something than (somehow) in the form of a pill. =P