The term energy is used by writers and practitioners of various esoteric forms of spirituality and alternative medicine to refer to a variety of phenomena. There is no scientific evidence for the existence of such energy.
Therapies that purport to use, modify, or manipulate unknown energies are thus among the most contentious of all complementary and alternative medicines. Claims related to energy therapies are most often anecdotal (from single stories), rather than being based on repeatable empirical evidence.
Concepts such as "life force" and "élan vital" existed from antiquity and emerged from the debate over vitalism in the 18th and 19th centuries with Mesmer and the magnetism. They continued to be discussed in the 20th century by some thinkers and practitioners in the modern New Age movement.
As biologists studied embryology and developmental biology, particularly before the discovery of genes, a variety of organisational forces were posited to account for their observations. German biologist Hans Driesch (1867–1941), proposed entelechy, an energy which he believed controlled organic processes. However such ideas are discredited and modern science has all but abandoned the attempt to associate additional energetic properties with life.
According to Brian Dunning, the scientific term energy is, in fact, misused in the context of spirituality and alternative medicine:
That's all that energy is: a measurement of work capability. But in popular culture, 'energy' has somehow become a noun. "Energy" is often spoken of as if it is a thing unto itself, like a region of glowing power, that can be contained and used. Here's a good test. When you hear the word "energy" used, substitute the phrase "measurable work capability." Does the usage still make sense? Remember, energy itself is not the thing being measured: energy is the measurement of work performed or of potential... Thus, this New Age concept of the body having an "energy field" is fatally doomed. There is no such thing as an energy field; they are two unrelated concepts.