As a Taoist cultivation method, "Inner Elixir" is relative to "Outer Elixir". Inner alchemy, as one of the main cultivation methods of Taoist priests, is mainly different from outer alchemy in that it does not melt gold, stone, lead, mercury and other drugs in a furnace cauldron to make pills for taking and eating, but practitioners can refine them into their own "pills" by taking their own bodies as the furnace cauldron and taking the essence in their bodies as medicine through a series of special cultivation methods. Because this kind of practice is mainly "homework" in the yogi's own body, it is called "Inner alchemy" practice. Taoism believes that through this kind of self-cultivation without borrowing foreign things, we can get the same effect as taking the elixir of life, and get the indestructible body, covering the world for a long time and not dying.

Inner alchemy inherits and synthesizes the techniques of ancient qigong, such as convincing, giving birth, keeping heart and thinking. At the same time, it also inherited and developed the ancient theories of essence, qi, theology and meridians. Based on the theory of Yin-Yang and divination in Zhouyi, it is a unique cultivation technique formed by M and the main cultivation method of Taoist priests after Song and Yuan Dynasties. There are different opinions about the origin of Neidan. Some people think it existed in the late Eastern Han Dynasty. Wei Boyang's "Zhouyi Shentongqi" is about inner alchemy. What he said is clearing away deficiency and damage, strengthening bones and benefiting qi, nourishing heart and calming nerves, strengthening bones and muscles, etc. They are all internal alchemy; Some people think that it existed in Wei, Jin, Southern and Northern Dynasties. For example, Huang Ting's Neijing's "wd Dance" is about Inner Dan, and even Xu Xun's "Lingjian Yanzi Fu Ji" in the Eastern Jin Dynasty says that "Inner Dan is used to serve the throat"; Some people also think that The Straight Road Written by Su, a famous Taoist priest in Sui Dynasty, is a book devoted to the study of Neidan. In any case, in the Tang Dynasty, there were more and more Taoist priests practicing Inner Dan, which was naturally related to the painful lesson that Taoist priests died of poisoning by Outer Dan in the Tang Dynasty.

In the late Tang Dynasty and the Five Dynasties, Neidan became a common practice among Taoist priests, resulting in Neidan's works such as Lingbao Dafa, Zhong You's Biographies, and Medicine Mirror. The theory and methods of Neidan were more abundant and systematic. Since the Song Dynasty, Inner alchemy has been divided into two factions: North and South. Based on the martial arts taught by the famous Taoist Zhang Boduan, Nanzong is mainly popular in southern Guizhou. Zhang Boduan's Five True Chapters is a classic of this school, which is characterized by advocating life first and then sex. Wang Zhongyang, the founder of Quanzhen Taoism, is the prime minister of the Northern Sect, and Taoist books such as Quanzhen Collection of Chongyang are the classics of the Sect, which is characterized by advocating double cultivation in life and taking cultivation as the first priority. Since then, there have been secondary schools founded by Taoist Li Daochun in the Yuan Dynasty, eastern learning founded by Taoist Lu Xixing in the Ming Dynasty and western learning founded by Taoist Li in the Qing Dynasty.

It is precisely because the inner alchemy is just an alternative cultivation method adopted by Taoist priests to avoid the cost of poisoning and death caused by the outer alchemy, so it is actually closely related to the outer alchemy. Generally speaking, "Inner alchemy" is nothing more than Taoist putting "Outer alchemy" into his body. In other words, the furnace tripod of Taoist alchemist is no longer a heavy guy made of metal, but his own body; The medicine of alchemy is no longer cinnabar, lead mercury and sulfur mercury, but essence, qi and spirit in the body. After a certain amount of cultivation (naturally, it is not an easy task), these three things are still called "elixir" (or "inner elixir" or "sacred fetus"), and their effects can make people live longer and even become immortals. Therefore, the inner alchemy basically follows the terminology of the outer alchemy. This shows that, from the internal principle, both external Dan and internal Dan are means for Taoist priests to seek immortality. Because of this, the cultivation of Neidan has become the main content of their daily life, and they all prefer to bear all kinds of hardships that must be paid in the process of cultivation. For Taoist priests in Neidan, although on the surface, it seems that there is no need to practice building a house, set a tripod to make a fire, wait in the Dan room to endure the invasion of cold and heat, and smoke with fireworks. It is even more difficult to really cultivate Inner Dan, which is far from effective in terms of time alone, so it can test a Taoist's faith and perseverance better than cultivating Outer Dan.