This not only discusses it, but has a link to the actual Phys Rev Letters paper. Jester (the blogger) thinks it may be a more mundane explanation than dark matter, but still an interesting one.
Neuro and cognitive science with the ultimate goal of understanding ourselves more fundamentally, and being able to do more effective treatment of mental disorders. Basically, reverse engineering the brain.
On the one hand, there is a good deal of abuse of these opioids. Their use needs close supervision to keep abuse down, and also trying to prevent accidental overdose.
On the other hand, drug enforcement laws enacted in the face of this abuse sometimes interfere with the legitimate treatment of chronic pain. There's a shortage of pain management specialists as they have to put up with more paperwork outside scrutiny and hassle since they have to prescribe such large amounts of opiates. A lot of young MDs make the decision to go into other areas due to that.
These are powerful drugs that should be available in the cases they are needed without causing difficulty for either the physicians or the patients who need them.