This article discusses the role of the precautionary principle within risk management systems for controlling the risks associated with chemical substances. The diversity of interpretation of the precautionary principle is highlighted in a comparative analysis between two divergent approaches to the principle: Canada's Chemicals Management Plan (CMP) and the European Union's Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH). The author suggests that, if appropriately applied, reverse onus – a stronger approach to the precautionary principle – is a more effective and efficient risk management tool for chemical regulation.