The same thing that happened when they made shipping nicotine through the mail illegal.

I stock up on a shitload of pure caffeine/nicotine, and store it.

Either that, or I start extracting it from other commonly available foods... (caffeine is present in quite a few foods naturally. )

Or, finally.... there would then just become a black market for caffeine.

The same stuff which happened during the prohibition period many years ago.