It is typically represented as a spherical pill of dark color and uniform texture, made of refined medical material.
The search for the pill was started several centuries BC ago and continued until 500 AD and was often based on noble metals such as mercury and gold.
[4] Taoist sects which advocated the attainment of immortality by consuming substances were very popular during the Eastern Han dynasty in the 2nd century AD and they were collectively known as the school of the "external pill", or Waidan (外丹).
[5] By contrast, "internal alchemy", or Neidan (内丹), was thought to create an immortal body within the corporeal body, and a variety of actions involving dietary, respiratory, and sexual practices and/or mental practices such as meditation were believed to cause immortality.
The writings of the Liexian Zhuan describes a man named Wei Boyang who had made such a pill of immortality.