What does that mean for you? It means that you are a morphine factory, probably designed by centipedes in moroccan genetic/firework laboratories for the sole purpose of providing narrative pleasures to a hyped up crowd of sycophantic lower mammals--rodents and marsupials mainly. The pressure in you head will only be relieved by the installation of a tap and hose system, allowing the golden nectar to be sucked directly from your cranium, providing the purest of transcendental bliss to the centipedes most wealthy of customers, the rat-bastard (excuse the pun) chipmunks landlords of the field.
Paging Dr. Benway.
It's not as interesting as all that, but it did make me think of my old friend Bill. Basically, the idea is that morphine is a naturally occurring neurochemical, like serotonin or dopamine. By giving patients a precursor to morphine as opposed to synthetic morphine, researchers are having success with the brain generating morphine by itself.. presumably at more exact levels than a shot could provide.
If you can stand it, it's probably best to read the paper from Proceedings of the National Academy of Sciences:
Endogenous formation of morphine in human cells -- Poeaknapo et al., 10.1073/pnas.0405430101 (abstract and full-text available)