Precaution is required when we govern actions that affect complex systems in which the consequences of progress and technology are poorly understood. Such complex systems include both our natural environment, where the widespread expansion of economic activity often introduces new and/or larger amounts of environmental toxins, and our own human biology, where poorly tested and documented health interventions championed by the medical industry can have unintended consequences. When such actions carry the potential for serious harm, the burden of proof lies on those arguing in favor of their safety and against evidence of harm. Furthermore, when these actions are medical, there is an even stronger social responsibility in favor of precaution, one that is enshrined in the Hippocratic Oath: first, do no harm. With the rising power of the medical industry and the growing pressure to defer authority to experts, there is an urgent need to strengthen our commitment to precaution and to reinforce our obligation to protect consumers, patients and victims from injury and abuses of power. In parallel, we must also defend the preference for more natural therapeutic modalities and nutritional choices in the face of scientific uncertainty.