Higher priced placebo analgesics are significantly more efficacious than lower priced placebo analgesics. This explains the popularity of high-cost medical therapies (eg, cyclooxygenase 2 inhibitors) over inexpensive, widely available alternatives (eg, over-the-counter nonsteroidal anti-inflammatory drugs) and why patients switching from branded medications may report that their generic equivalents are less effective.
82 healthy paid volunteers were recruited using an online advertisement. Each participant was informed by brochure about a (purported) new opioid analgesic approved by the Food and Drug Administration; it was described as similar to codeine with faster onset time, but it was actually a placebo pill.
After randomization, half of the participants were informed that the drug had a regular price of $2.50 per pill and half that the price had been discounted to $0.10 per pill. All participants received identical placebo pills and were paid $30. Participants were blinded to the study purpose, and researchers were blinded to group assignment.
Electrical shocks were applied to the wrist. They were calibrated to the pain tolerance for each participant. Next the participants had to rate the pain on a visual analogue scale. Shocks up until this pain level were then applied. After the first shock a placebo analgesic was given. This was followed by the same pain stimulus. After each shock the participants had to score their pain.
In the regular-price group, 85.4% (95% confidence interval [CI], 74.6%-96.2%) of the participants experienced a mean pain reduction after taking the pill, vs 61.0% (95% CI, 46.1%-75.9%) in the low-price (discounted) group (P = .02). Similar results occurred when analyzing only the 50% most painful shocks for each participant (80.5% [95% CI, 68.3%-92.6%] vs 56.1% [95% CI, 40.9%-71.3%], respectively; P = .03).
These findings need to be replicated in broader populations and clinical settings to better understand how communicating quality cues with patient populations can maximize treatment benefits and patient satisfaction.
Other possible influences on efficacy I can think of are: color, brand, advertisement.
Any other suggestions?