Chinese traditional medicine postulates seven modes by which drugs (natural products) can elicit pharmacologic effects, one when an agent is used alone and six when several are used in combination. In the latter instance, the combined products in a prescription can interact with each other to augment or reduce potency or intrinsic activity with respect to beneficial or harmful effects. Such intuitive insight was derived from skillful clinical observations made by the ancient attending physician without the aid of instrumentation such as the stethoscope, thermometer and sphygmom-anometer. The prescribing followed external methods of diagnosis involving inspection, ausculation, olfaction, and interrogation coupled with palation and pulse feeling. It is most illuminating, therefore, that the six types of drug interactions conceived from clinical applications by Zhang Zhong-Jing and Tao Hong-jing almost two millennia ago can be utilized to explain contemporary proposed modes of agonistic and antagonistic actions between chemical substances derived from quantitative experimental measurements. Examples will be given with respect to how xiang xu 相須， xiang shi 相使，xiang wei 相畏， xiang wu 相惡， xiang sha 相殺 and xiang fan 相反 can be incorporated into mechanistic Western terminology for producing beneficial or harmful effects associated with additive, synergistic, enzyme inductive, partial agonistic, competitive or non-competitive antagonism and pharmaceutic incompatibility properties.