That is my point. Oral Methadone works just fine. Although, BA technically can range from 40-95%, however manipulating PH pretty much guarantees high BA, mild-moderate enzyme inhibitors can yield well over 90%, and a longer half-life.
To the user below:
As I said, high dose IV Methadone CAN produce a surprising rush, especially if there is already some in your system.
But on MMT, tolerance gets so high it would be pointless. Faster onset, but you'd need a 5ml syringe.
I cannot think of a single opioid(or really a good benzo*) that works effectively SL, except buprenorphine, and even it has fairly low-moderate BA, unless you dissolve it in water, and then 50% at best.