Causality is a core concept in medicine. The quantitative determinacy characterizing today's biomedical science is unprecedented. The assessment of causal relations in human diseases is evolving, and it is therefore fundamental to keep up with the steady pace of theoretical and technological advancements. The exact specification of all causes of pathologies at the individual level, precision medicine, is expected to allow the complete eradication of disease. In this article, we discuss the various conceptualizations of causation that are at play in the context of randomized clinical trials and observational studies. Genomics, proteomics, metabolomics and epigenetics can now produce the precise knowledge we need for 21st century medicine. New conceptions of causality are needed to form the basis of the new precision medicine.