The Dutch self-regulatory body for pharmaceutical advertising, CGR, has, over the past years, developed standard case law pursuant to which comparative claims may only be made if reference is made to at least two independent comparative clinical studies that substantiate the claim.

In March 2009, the CGR issued Guidelines on the substantiation of comparative claims, which will enter into force on 1 January 2010. In these new guidelines, the CGR abandons the "2 studies criterion": comparative claims will need to be substantiated by at least one study and not necessarily by two. The study that is used to substantiate the comparative claim must have been published in a peer-reviewed journal and must be of sufficient quality and authority.