Physical possession but not psychological possession of a placebo enhances placebo analgesia

Research on placebo analgesia usually shows that people experienced pain reduction after "using" a placebo analgesic. An emerging line of research argued that "merely possessing" a placebo analgesic could induce placebo analgesia under some circumstances (Yeung, Geers, & Kim, 2019; Yeung, Geers, & Colloca, 2020; Yeung & Geers, in press). These research reported that participants who merely possessed (vs. did not possess) a placebo analgesic showed greater pain resilience. The current study aims to clarify the "nature" of analgesic possession, investigating whether physical possession of a tangible placebo analgesic or psychological possession of it via a coupon yields better pain outcomes. Healthy participants (N=90) were presented with a vial of olive (placebo) oil purportedly claimed as a blended essential oil that blocks pain upon nasal inhalation. They were randomized to either physically possess it (physical-possession condition), or possess a coupon to exchange for it (psychological-possession condition) or not possess it (no-possession condition). Participants did a cold-pressor-test and their objective physical pain responses (pain threshold and tolerance) and subjective psychological pain perception (pain intensity, severity and quality) were measured. Results indicated that participants in the physical-possession condition showed better physical pain outcomes than participants in the psychological-possession and no-possession conditions. All participants did not show significant differences in their subjective self-reported pain outcomes. The finding answers a fundamental question about the relative benefit of immediate tangible medication possession over delayed medication possession via prescription. It provides important insights to clinical practice.