Although I cannot speak on this topic with as much certainty as others, a friend of mine is currently on a Suboxone prescription for an oxycodone addiction, and to the extent of my knowledge it seems that the buprenorphine and methadone would cancel one another out; the latter's efficiency would be reduced significantly by the former as methadone, being a full µ-opioid agonist, will not be able to bind to the receptors that buprenorphine exhibits its blockade effect on, the latter of which binds tightly to µ-opioid receptors as only a partial agonist.
If the buprenorphine is administered a duration of time after the methadone, however, the effects may be desirable to achieve a high of some sort.
On the other hand, Suboxone will exhibit naloxone's competitive antagonist properties on the µ-opioid receptors, for which it possesses a high affinity. So if you're looking to combine methadone with your suboxone maintenance dosage, you're sorry out of luck; the addition of naloxone (which is present for this precise reason) changes things just a bit.
This is all pure conjecture with my knowledge of pharmacology, but if you're on Suboxone I highly doubt you'll be able to obtain any level of opiate high with relative ease. Smoke some tree!
The Doctor
