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I was reading about the morphine molecule. It binds to our opioid receptors. These opioid receptors have endogenous binding partners also, like β-Endorphin. There have been reports that these endogenous receptors have a different impact on opioid receptors than exogenous opioids (morphine). Source

I couldn't find any trials of intravenously administered β-Endorphins for pain relief. Although there are reports of using intravenous β-Endorphins on mice (1976), monkey (1989) and schizophrenia patient (1980).

Am I missing something? Is it possible to use endogenous opioids?

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  • I suspect it has something to do with the molecules' half-lives, but I don't have any references at the moment. I seem to recall that endorphins are metabolized fairly quickly.
    – MattDMo
    Jun 23 at 18:02
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One of the reasons is stability. According to this paper from 1979, the half-life of β-endorphin in 3 patients was measured at 37 minutes. This is in contrast to morphine, which has an elimination half-life of 3-4 hours (source). This means that while β-endorphin may have some use in short-term situations like surgical recovery rooms, it wouldn't really be appropriate for longer-term use where it's helpful to have doses more spread out.

Endorphins are also not very good candidates for oral pain therapy. Oral morphine does exist, but its bioavailability is significantly lower than IV due to degradation in the gut before absorption into the blood stream, meaning higher dosages are needed for equivalent pain relief. Seeing as endorphins are just polypeptides, I would imagine that they'd be severely degraded by proteases before being absorbed, requiring even higher doses to achieve pain relief that doesn't even last very long.

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