The view that a whole plant, as a complex mixture of compounds, can behave as a different and often safer agent than any single molecule isolated from it.
Tensions
Isolation gives precision, reproducibility, and patentability, and sometimes a clean compound beats the raw plant (aspirin over willow bark). But isolating the famous component can collapse interest in everything else in the plant and produce a harsher, narrower drug than the mixture the body can modulate.