Wow, someone actually gets it...

Steroids are a whole diff. class of "medicine".
Nothing like vitamins. The use has to be
regulated closely because they are fat soluble
and spend much more time in cells unlike the vast
majority of vitamins (just urinated out)
and like most of the other chemicals
that are not banned and keep horses healthy.

The of level hormones are very important because they interact
very strongly when compared to the conc. of other hormones produced naturally.
Ask any vet or doc.

But if rules are going to be made they have to be able to tell
if they are violated first (which is a huge problem because guidelines
that are measurable and acceptable by all have to be produced, good luck with that). And then there must be a punishment
that hurts.