The more general deeply-entrenched golden goose here is branding, which applies to much more than OTC medicines. Make it so the active ingredients have to be listed prominently - the largest text on the front of the product package - and these concerns diminish greatly.

It would also fix the homeopathic snake oil as well, which has started showing up as options in previously-reputable medicine aisles. So at any rate, be on guard if you don't want to end up accidentally buying a bottle of water plus flavoring in your cold-addled state.