No offense, but I'd like to point out that meth is an upper like cocaine and other stimulants and heroin is a depressant similar to barbiturates, although not as sleep inducing.
AN OATH IS FOREVER
You are right. But you are using a rational brain.
Whether an up or a down is the interest of a tweaker, not an addict. An addict suffering withdrawal from pain killers which he can no longer acquire is going to get relief the quickest, easiest and cheapest way possible. Meth fills that bill. That the relief is contra-indicated, doesn’t last all that long and causes an even more painful crash means nothing. He will just get and use more. The euphoria is the only goal. Once meth became difficult to manufacture, heroin comes to fill the void.