[kevinmchugh]

If a drug is compatible with a healthy social or productive lifestyle it would seem unreasonable to ban it. Danger of withdrawals might be a consideration.

Caffeine is pretty safe. The withdrawals, for those of us who experience them, are safe if unpleasant.

There's prescription drugs that cause dependency but are widely prescribed. Gabapentin is a good example?

Alcohol is the drug that best fits the "grandfathered" idea, since it's for many folks not compatible with a healthy lifestyle and the withdrawals can be fatal. Alcohol is impossible to ban, though, because the precursors are in every grocery store on the planet and grow on trees

[inigyou]

There are many prohibited substances that are more "compatible with a healthy social or productive lifestyle" than legal substances. The actual criteria for a ban seems to be if it isn't alcohol, caffeine, nicotine, or prescribed by a doctor.