Boosting Open-Label Placebo Effects in Acute Induced Pain in Healthy Adults

Pain is highly prevalent in hospital settings. Standard systemic treatment for acute pain consists mainly of basic analgesia. The use of these drugs is often restricted due to their contraindications. Placebo is used nowadays to describe sham treatments and "inert" substances like sugar pills and saline injections. Placebos are proven to elicit clinically significant effects in various conditions, including pain. Ethical concerns about the use of deceptive placebos have prevented their implementation in clinical practice. A possibility to address this issue would be to prescribe placebos openly, that means, without deception. This randomized crossover study evaluates the efficacy of open-label placebo (OLP) in acute pain. Subjective pain ratings and areas of hyperalgesia and allodynia will be measured in a well-established experimental pain model (intradermal electrical stimulation model evoking pain: this installation will apply monophasic, rectangular electrical pulses of 0.5ms duration with alternating polarity at 2 Hz frequency. The current will be increased to target a pain rating of 6 of 10 on the NRS (0 = no pain, 10 = worst imaginable pain). Three further adjustments in current will be made every 5 minutes for the next 15 minutes to compensate for habituation. This final current will be kept constant until the end of the particular experiment) and analgesia elicited by OLP injections will be investigated.

In Part 1 duration of OLP analgesia will be examined, and onset and size of the effect will be reevaluated.

In Part 2 of this study outcomes between subjects receiving one OLP injection, subjects receiving one repetition of the injection on a fixed time point and subjects receiving one repetition of the injection on-demand will be evaluated (which leaves the last group a choice over when they would like to have the placebo "booster").

Inclusion criteria

• Healthy volunteers (ASA Class I or II), aged 18 to 65 years
• BMI between 18 and 25kg/m2
• Able to understand the study and the NRS
• Able to give informed consent

Exclusion criteria

• Participation in a previous open-label placebo study; for Part 2, this includes Part 1 of this study
• Regular intake of medications or drugs potentially interfering with pain sensation (analgesics, opioids, antihistamines, calcium and potassium channel blockers, serotonin/ noradrenaline reuptake inhibitors, corticosteroids)
• Neuropathy
• Chronic pain
• Neuromuscular disease
• Dermatological disease (i.e. Atopic Dermatitis)
• Psychiatric disease
• Pregnancy / Lactation