There is no law of unintended consequences: positive unintended consequences in injury prevention.

Since the turn of the century, there has been a drumbeat among those opposed to regulations, including safety regulations, to talk about a "law" of unintended consequences. The law claims that regulations commonly have large negative unanticipated effects. But in the injury prevention field, regulations actually seem to have few such large negative unintended consequences and many positive unintended consequences. This essay describes a half dozen instances of beneficial unanticipated consequences that appear to have been caused by regulations, such as that motorcycle helmet laws not only reduced head injuries to cyclists but also seem to have reduced the theft of motorcycles; a higher minimum legal drinking age not only reduced motor vehicle deaths for those aged 18-20 but also likely reduced suicides among that age group; a successful Air Force suicide prevention initiative not only reduced suicide but also seems to have reduced interpersonal violence and seat belt laws not only increased seat belt wearing but also appear to have increased positive attitudes about both seat belt use and mandatory seat belt laws. The "law" of unintended consequences seems similar to "Murphy's Law" (ie, anything that can go wrong will go wrong) in that while both laws correctly warn that policymaker overconfidence can lead to unwanted and detrimental outcomes, both are less similar to empirical laws than they are to humorous adages that are usually incorrect. While there are many actual empirical economic "laws", the "law" of unintended consequences does not appear to be one of them.