I'm being tongue-in-cheek. That is, the effectiveness of the medicines would be very different, but the actual substances available in some way would barely be different.
With the exception of marijuana, almost every drug with medicinal use is either available medically in some form or unavailable, but with very related 'cousins' readily available.
Marijuana is available as Marinol - it just doesn't work, because it's synthesized without the full set of ~70 cannabinoids. MDMA isn't available (outside of very restricted research), but it's closely related to methamphetamine, which is available with a prescription. (People are often surprised to hear that one). GHB is available with a prescription. Heroin is really just a synthesized and concentrated form of morphine (available with prescription), and peyote is available for some religious ceremonies. [Psilocybin is not, but oddly enough, I believe mushroom spores are legal, even though the mushrooms are not (because the spores don't contain any psylocybin - I believe this may depend on your jurisdiction, though, and as always, IANAL.).]
So what's the end result? We've criminalized drugs not based on their underlying chemistry - there is almost no Schedule I drug that doesn't have a closely related (and oftentimes identical!) counterpart in Schedules II-IV or not scheduled at all.
If I were the conspiracy-theory type, I'd say that this is a way of saying that drugs can only be useful if a pharmaceutical company is profiting off of it. Though I'm inclined to side with Hanlon's razor on this one - that's not really how it came about historically, even if 'Big Pharma' does benefit off of it now. I don't really care - I just wish we'd start drafting laws based on science, not fear.