Oxytocin and the placebo effect

INTERVENTION: A randomized, placebo‐controlled study design is used. After initial screening, participants take part in one study visit in which they are randomly allocated to one of four groups: 1) oxytocin group with positive suggestions, 2) oxytocin group without positive suggestions, 3) placebo group with positive suggestions, 4) placebo group without positive suggestions. Participants perform a baseline CPT (Cold Pressor Test) on which their pain sensitivity and unpleasantness ratings are measured. Subsequently, participants are administered an oxytocin or placebo spray. In the oxytocin with positive suggestions and oxytocin without positive suggestions groups, participants receive a 24 IU dose of oxytocin via a nasal spray. In the placebo groups, participants receive a placebo spray. Participants in two groups (oxytocin with positive suggestions group and placebo with positive suggestions group) additionally receive positive verbal suggestions about the expected analgesic and itch‐relieving effects of oxytocin. After a waiting period for the oxytocin to take effect, a second CPT is performed. The session finishes with transdermal HI (histamine iontophoresis) after which itch ratings, wheal size, and skin temperature are measured. Additionally, questionnaires are administered to assess positive and negative affect, personality and expectations amongst others. CONDITION: Placebo effect, Oxytocin ; ; PRIMARY OUTCOME: The main study outcome is the difference between the oxytocin with positive suggestions group (group 1) and the placebo with positive suggestions group (group 3) on self‐reported pain ratings and on self‐reported itch ratings. Self‐reported pain will be assessed in response to the CPT after the intervention controlled for the baseline CPT self‐reported pain ratings. Self‐reported itch ratings will be assessed in response to HI. SECONDARY OUTCOME: • The difference between the oxytocin without positive suggestions group (group 2) and the placebo without positive suggestions group (group 4) on self‐reported pain and itch ratings in response to the CPT and histamine test to investigate the effects of oxytocin on pain and itch sensitivity ; ; • The difference between the placebo with positive suggestions group (group 3) and placebo without positive suggestions group (4) on self‐reported pain and itch ratings in response to the CPT and histamine test to investigate the effects of verbal suggestions on pain and itch sensitivity ; ; INCLUSION CRITERIA: 1. Healthy female volunteers between 18 and 35 years old; 2. Good understanding of written and spoken Dutch.