I was hoping somebody could explain (in fairly simple terms) why using heroin on top of subutex is not recommended and why we change people over to methadone if they are consistently using on top of their subutex prescription?
High doses of subutex 12-16mg block the opiate receptors. If people use Heroin on top it has little effect. To get an effect people have to not take the subutex and then it probably ends up on the streets.
The NICE guidelines show Methadone has slightly better outcomes over buprenorphine and people tend to get more of an opiate effect from it.
People who want to feel a bit drowsier tend to prefer methadone.
People can use on top of Methadone and not need to omit the dose.
And occasionally people who don't realise the blocking effect of high doses of Subutex increase their heroin usage and stop using the Subutex at the same time, with tragic consequences.
As was mentioned Subutex, or more accurately buprenorphine HCL, has a very high affinity for the mu opioid receptor. This affinity is much higher than that of heroin and other short acting mu agonist opioids (like morphine for instance) and as such it has a blocking effect on the receptor. In short, the desired effects brought about by mu opioid receptor agonists, euphoria being chief among these, are no longer felt. Furthermore, the buprenorphine vacates the receptors at a very slow rate and as a result it usually requires skipping several doses over a period of a few days before the euphoric feeling brought about by using heroin begins to return.
While methadone exhibits a "blocking" effect in high doses, this is actually just a function of cross-tolerance across other opioids and is more easily overcome by using a higher than usual dose of heroin, something that is impossible while taking high doses of buprenorphine.
So in short, they switch so that they can still "get high".
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