Objective: We tested a novel intervention for reducing demand for ineffective health remedies. The intervention aimed to empower participants to overcome the illusion of causality, which otherwise drives erroneous perceptions regarding remedy efficacy.

Design: A laboratory experiment adopted a between-participants design with six conditions that varied the amount of information available to participants (N = 245). The control condition received a basic refutation of multivitamin efficacy, whereas the principal intervention condition received a full contingency table specifying the number of people reporting a benefit vs. no benefit from both the product and placebo, plus an alternate causal explanation for inefficacy over placebo.

Main outcome measures: We measured participants’ willingness to pay (WTP) for multivitamin products using two incentivized experimental auctions. General attitudes towards health supplements were assessed as a moderator of WTP. We tested generalisation using ratings of the importance of clinical-trial results for making future health purchases.

Results: Our principal intervention significantly reduced participants’ WTP for multivitamins (by 23%) and increased their recognition of the importance of clinical-trial results.

Conclusion: We found evidence that communicating a simplified full-contingency table and an alternate causal explanation may help reduce demand for ineffective health remedies by countering the illusion of causality.