Regarding talk about the analgesic properties of THC
receptors and opiod receptors, I doubt that is the only or
even the primary function of either of these receptor systems.
Every ligand and every receptor system has numerous different
functions in different parts of the body and nervous system.
The (possibly) numerous ligands for both opiod and THC receptors
probably modulate neural activity to a very fine degree and
have different effects depending on which areas, synapses, etc.
we're dealing with. Just because drugs that act on these
receptors have a certain effect, I wouldn't assume the endogenous
ligands serve a similar purpose. Remember, all drugs are sloppy
and the endogenous ligands are probably MUCH more precise.