When I read this, I said, out loud, "What the flying farkmipple?"
So does naloxone block placebo effects in general, or only placebo morphine? Inquiring minds want to know.
Check out a good lecture on pain at http://www.youtube.com/watch?v=gQS0tdIbJ0w for more context.
Naloxone blocks placebo analgesia in general. I can dig up the referenced papers if you don't have access.