Traditional Chinese Medicine (TCM) is a medical system from China over two thousands years ago. TCM theory is based on Qi (energy) and teaches that health is the result of the internal balance of Yin and Yang. The differences between TCM and Western biomedicine are rooted in how medical conditions are represented. TCM often represents a medical condition with a metaphor. For example, Western biomedicine represents the condition of a headache in terms of overactive pain receptors or vasoconstriction of cerebral blood vessels, but in TCM, a headache is represented as a syndrome such as Wind-Cold or Hyperactivity of Liver Yang.