The role of placebo effects in mindfulness-based analgesia

Abstract

Mindfulness meditation produces small to moderate improvements in acute and chronic pain relative to passive controls. However, effects are smaller when mindfulness is compared to an active control, raising the possibility of placebo effects. This thesis sought to develop a theoretically derived and specifically matched sham (placebo) mindfulness control to determine whether placebo effects contribute to mindfulness-based analgesia and how they might interact with mindfulness-specific effects. In Study 1, we developed a sham that matched mindfulness on credibility and expectancy but did not activate mindfulness-specific processes. Both mindfulness and sham equally increased acute pain tolerance relative to no treatment, an effect most strongly associated with expectancy. In Study 2, we used the sham to examine the effects, mechanisms and interactions between mindfulness and placebo effects in a balanced placebo design that manipulated treatment (mindfulness, sham) and expectancy (told mindfulness, told sham). Both mindfulness and sham equally reduced acute pain intensity and unpleasantness, and increased pain tolerance relative to no treatment. Expectancy fully mediated the effects on pain unpleasantness and pain tolerance, but no specific effects nor interactions with mindfulness were observed. In Study 3, we examined the role of sham specificity in an online mindfulness intervention for chronic pain. We found that mindfulness, our specifically matched sham, and a generally matched sham equally reduced chronic pain unpleasantness relative to audiobook control. Effects on pain were again most strongly associated with expectancy. Overall, across the three studies, mindfulness failed to outperform sham on any pain outcome. Further, mindfulness and shams equally engaged cognitive and affective processes in a pattern consistent with the placebo effect. These findings provide the first clear evidence that placebo effects contribute to mindfulness-based analgesia.