Endogenous opioids and placebo analgesia

Steve Palmer spalmer at mdanderson.org
Thu Jan 27 10:21:45 EST 2000


    My name is Stephen Palmer, and I am a postdoc at the Dept. of Pain
Research at the M.D. Anderson Cancer Center, having recently defended my
dissertation at SUNY Stony Brook.
    I am writing the group because my dissertation produced results I can't
explain, and I am wondering if any of you have any suggestions about what
may have occurred .  My dissertation addressed the subject of placebo
analgesia and endogenous opioids.  Previous research has found that placebos
can alleviate various kinds of pain, but that naloxone (an opioid
antagonist) can reverse or weaken placebo analgesia.
    My study was intended to be a replication and extension of the previous
research.  I used a 2x2 design in which all subjects received an intravenous
infusion, but half were told that they would receive a potent pain reliever,
while the other half were told that they would only get saline.  In
actuality, some subjects received saline while others got naloxone.  Cold
pressor tests (a pain tolerance task) were given before and after the
infusion.
    What I expected what that subjects who were told to expect a pain
reliever but who got saline instead would show a reduction in pain (i.e.
placebo analgesia).  Subjects who got the pain reliever message plus
naloxone, on the other hand, would show no change in pain, or at least a
smaller reduction than the pain reliever/saline group.  The groups who were
told they were getting only saline (and really got either saline or
naloxone) would show no change.
    This didn’t happen.  Instead, only the pain reliever/naloxone group
showed pain relief!  The other three groups showed either no change or
increased pain.  This finding is unlike anything in the prior literature,
and I have no explanation for it.
    My question to you is, is there any literature out there which can
explain these findings?  Are there any other studies, perhaps unpublished
ones, which have found the same results?  I would appreciate any input you
could give.






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