DrugBuyers.Com: Re: Breakthrough pain meds.

Sarah-
Methadone reduces or eliminates the effectiveness of other opiates because it is long acting. If I remember right, you take your methadone in 3 doses throughout the day. A single dose of methadone has a half-life of about 12-24 hours. Essentially, think of your opiate receptors as a sponge, on methadone they get saturated for a long time, so when you attempt to use a different narcotic, there is simply no place for it to get absorbed. On a three-times-a-day dosing regimen, you wouldn't get much relief at all from, say, Oxycodone. If you were on a once daily dosing regimen, you may get relief towards the end of the day from oxy if you took the methadone early in the morning.
The higher your methadone dose, the less effective other narcotics (including heroin for those on MMT) will be. In fact, even though the breakthrough med may not FEEL like it is doing any good, it's CNS depressive qualities are still adding to those of the methadone and people can overdose without ever achieving a "high" or analgesia.

Hope that explains it a bit better.

All the best---
night_shade

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Never underestimate the predictability of stupidity.