With designer drugs, scientists can't agree on what exactly a 'drug analogue' means, so an analogue law would be unenforceable. All drugs invented after, say, 1950 without FDA approval could be banned; but then trade of the drug wouldn't be prosecutable until it were proven that it's artificial and invented; if it were naturally occurring (say, from Psilocybin mushrooms) then it can only be discovered and not invented. The drug scheduling works as a blacklist, but could be reworked to only allow whitelisted drugs.
A law targeting artificially-created drugs or GMO-created drugs would be unenforceable. Many pharmaceuticals are mass-produced nowadays with genetically-engineered organisms (fungi, often) that secrete the target chemical. There's no way to always distinguish a GMO from a crypto-organism, or in other words, an artificially-created drug factory from a naturally-occurring drug factory. Therefore, there'd be no way to prove that a drug was made artificially rather than naturally. So White-listing could still stop trade, but that'd only work until...
Homebrew. As genetic modification tech gets cheaper and easier to use, there will be cheap DIY kits to make your own designer drugs and the organisms to produce them. Later, easily-obtainable underground apps will help you design drugs with certain target effects, based on (but sufficiently modified from) existing recreational drug molecules. Once the international effort to use supercomputers to model the human body's physiology gains open access, people can submit potential molecules to the system and see their effects (and side-effects). No 30-year studies with methodology errors mixed with decades of FUD and hand-wringing, just the truth in black and white for everyone to see. New molecules that aren't simply modified versions of existing chemicals can be brute-forced that have certain effects, avoiding any existing analogue laws. This will enable an explosion in the effectiveness and safety of designer drugs, as there's an uncomfortable (to some) overlap with the effects of medicinal pharmaceuticals, leading to the end of support for drug restrictions.