We found no evidence that consumers benefit from government-mandated disclaimers in advertising. Experiments and common experience show that admonishments to change or avoid behaviors often have effects opposite to those intended.We found 18 experimental studies that provided evidence relevant to mandatory disclaimers. Mandated messages increased confusion in all, and were ineffective or harmful in the 15 studies that examined perceptions, attitudes, or decisions. We conducted an experiment on the effects of a government-mandated disclaimer for a Florida court case. Two advertisements for dentists offering implant dentistry were shown to 317 subjects. One advertiser had implant dentistry credentials. Subjects exposed to the disclaimer more often recommended the advertiser who lacked credentials. Women and less-educated subjects were particularly prone to this error. In addition, subjects drew false and damaging inferences about the credentialed dentist.