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Patients
with post-herpetic neuralgia were given oral doses of clonidine,
codeine, ibuprofen, or lactose placebo (from Max et al., 1988b).
The three drugs tested produced little or no analgesia relative
to placebo (not shown), so data from all treatments are represented
here to illustrate the association of pain relief with side
effects. Summed pain relief over 6 hours is plotted against
a total side effect score obtained by summing all hourly reports
of adverse effects, each rated on a three-point scale. Patients
who reported any side effect, even if slight effect, which
we thought was "side effect-triggered placebo analgesia",
did not increase at higher total side effect scores. If confirmed,
this result would suggest that if a drug showed a positive
dose-response curve for analgesia above the dose level where
most patients have at least mild side effects, one could infer
that analgesia was due to a specific effect on pain mechanisms,
not just an "active placebo" effect.
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