Placebo effects relieve pain but it is yet unclear how they can be enhanced to maximize positive treatment outcomes. Oxytocin may potentially be a mediator of the placebo effect due to its trust enhancing and stress relieving actions. In two studies, we investigated the influence of oxytocin on placebo analgesia and hyperalgesia. In the first study, 108 female participants were allocated to one of four groups: oxytocin with positive verbal suggestions, placebo with positive verbal suggestions, oxytocin without suggestions, and placebo without suggestions. The administration of 24 IU oxytocin or a placebo spray was preceded by positive verbal suggestions regarding the pain-relieving properties of the spray or no suggestions. Pain was assessed with a cold pressor test. In the second study, 80 male participants were allocated to an oxytocin or a control group. After the administration of 40 IU of oxytocin, they received verbal suggestions regarding a sham electrode that was said to increase or decrease their pain sensitivity depending on the mode indicated by a visual cue. To induce and test placebo analgesia and hyperalgesia, a conditioning task was used in which visual cues indicated low, medium or high heat pain. Positive verbal suggestions and a combination of suggestions and conditioning induced significant placebo analgesia and hyperalgesia. No evidence was found that  oxytocin influences placebo effect, using female and male samples and also different dosages of oxytocin. Future research should focus on other possible mediators of the placebo effect such as, for example, vasopressin or  other pharmacological agents.

01 - CAN OXYTOCIN INFLUENCE PLACEBO AND NOCEBO EFFECTS IN PAIN?