I beg to differ with you Cantrell, it is in the class of opioids, look it up if you don't believe me. And yes it does bind with the opiate receptors. Also,
Codeine is not synthetic. That's three strikes, you're out.
"Propoxyphene acts as a weak agonist at OP1, OP2, and OP3 opiate receptors within the central nervous system (CNS).
Propoxyphene primarily affects OP3 receptors, which are coupled with G-protein receptors and function as modulators, both positive and negative, of synaptic transmission via G-proteins that activate effector proteins."
http://www.mongabay.com/health/medic.../Darvocet.html