The authors examine the problem of defining alternative medicine, and after a brief analysis conclude that a satisfactory unifying definition of the different practices is not possible. Scientific knowledge is a function of scientific method. In turn the principle of falsifiability proposed by Karl Popper is used as a demarcation line between science and pseudoscience. They assert that the various alternative modalities do not represent authentic scientific disciplines, as they lack many of the minimum requirements of scientific discourse and, above all, because they violate the principle of falsifiability. Until they overcome these methodological shortcomings, alternative medical practices cannot become authentic scientific disciplines.