In this article, it is argued that uncertainty and risk are intermingled and that this has severe consequences for risk regulation. First, uncertainty and risk are considered in the context of the precautionary principle from a theoretical point of view. On the basis of an interdisciplinary reflection, it is concluded that a paradox can be observed. Subsequently it will be investigated how this so-called uncertainty paradox works out in practice. This will be done by analysis of the Pfizer case, situated at the EU level. In this case, that related to the use of antibiotics as a growth promoter in the production of meat, the precautionary principle was used as policy and legal principle. The analysis will detail the regulatory complexities that result from the contradictions in precautionary thinking. In conclusion suggestions will be advanced for regulatory reform in the broader sense, including the role of experts, and an interdisciplinary research agenda will be proposed.