[tacticalogic]

If Substance A was legal, are you saying we'd see no change whatsoever in the use of Substance B?

No, I'm saying that we'd see no change in the pre-disposition to use Substance B. If whatever is causing the pre-disposition to want to use Substance A also causes a pre-disposition to use Substance B, legalizing or criminalizing Substance A is not going to change whatever is causing the pre-disposition.

[robertpaulsen]

But what if the legalization of Substance A resulted in more users of Substance A? Let's just say the use doubled.

Certainly some of those would go on to Substance B? But you're claiming no increase.