In the Western world, those who are interested in Neidan (Internal Alchemy) sometimes claim that the Daode jing (Scripture of the Way and Its Virtue) is a Neidan text.
This view deserves attention, because it is in some respects similar to the traditional view held by Neidan masters and adepts in China. However, it also requires some comments.
While Neidan needs the Daode jing, the Daode jing does not need Neidan. The Daode jing is an integral statement of Taoist doctrine. Being complete and self-contained, it does not demand or await anything outside itself. Its doctrine, however, can be applied, to varying extents, to different practices, arts, and sciences. The Daode jing itself pays much attention to one particular application of its own doctrine: the art of government.
Since some fundamental principles of Neidan are based on the doctrine of the Daode jing, a Neidan practitioner might claim that the Daode jing is a Neidan text. But for a similar reason, an army general who practices the "art of war" might claim that the Daode jing is a text about making war.
Then, is the Daode jing about Neidan or about war? It is neither about Neidan nor about war — but its teachings can be applied to an indefinite number of fields. Neidan is one of those fields.
In other words, the Daode jing contains the main statement of doctrines that are fundamental in Neidan, but is not "a Neidan text" of its own.
Consider, for example, the famous passage found in section 42, which describes the relation of the Dao to the cosmos using a sequence of stages: "The Dao generates the One, the One generates the Two, the Two generate the Three, the Three generate the ten thousand things". Neidan masters of all times have applied these words to the Neidan practice, which goes through that sequence in reverse in order to "return to the Dao". Does this mean that the Daode jing describes the Neidan practice?