Conservationists have long sought to reduce consumer demand for products from overexploited wildlife species. Health practitioners have also begun calling for reductions in the wildlife trade to reduce pandemic risk. Most wildlife-focused demand reduction campaigns have lacked rigorous evaluations and thus their impacts remain unknown. There is thus an urgent need to review the evidence from beyond conservation science to inform future demand-reduction efforts. We searched for systematic reviews of interventions that aimed to reduce consumer demand for products that are harmful (e.g., cigarettes and illicit drugs). In total, 41 systematic reviews were assessed, and their data extracted. Mass-media campaigns and incentive programs were, on average, ineffective. While advertising bans, social marketing, and location bans were promising, there was insufficient robust evidence to draw firm conclusions. In contrast, the evidence for the effectiveness of norm appeals and risk warnings was stronger, with some caveats.