BACKGROUND: Recent evidence supports the beneficial effects of mindfulness meditation on pain. However, the neural mechanisms underlying this effect remain poorly understood. We used an opioid blocker to examine whether mindfulness meditation-induced analgesia involves endogenous opioids. METHODS: Fifteen healthy experienced mindfulness meditation practitioners participated in a double-blind, randomized, placebo-controlled, crossover study. Participants rated the pain and unpleasantness of a cold stimulus prior to and after a mindfulness meditation session. Participants were then randomized to receive either intravenous naloxone or saline, after which they meditated again, and rated the same stimulus. RESULTS: A (3) × (2) repeated-measurements analysis of variance revealed a significant time effect for pain and unpleasantness scores (both P <.001) as well as a significant condition effect for pain and unpleasantness (both P <.2). Post hoc comparisons revealed that pain and unpleasantness scores were significantly reduced after natural mindfulness meditation and after placebo, but not after naloxone. Furthermore, there was a positive correlation between the pain scores following naloxone vs placebo and participants' mindfulness meditation experience. CONCLUSIONS: These findings show, for the first time, that meditation involves endogenous opioid pathways, mediating its analgesic effect and growing resilient with increasing practice to external suggestion. This finding could hold promising therapeutic implications and further elucidate the fine mechanisms involved in human pain modulation.