Japkasai is an ancient massage therapy, so it has no side effects. Oriental medicine refers to Chinese medicine in a narrow sense, and traditional medicine in Asia in a broad sense, but Japkasai is a well-established traditional remedy raised in Southeast Asia based on the theory of oriental medicine. By stimulating the energy line (like a meridian) called "Sen" in Thai traditional medicine, it regulates the energy (flow of qi) called "Prana" that flows throughout the body. Of course, it has a local purpose, but since it is done while approaching the whole body, it is not just a matter of "pulling a lot". There are some people who order a lot of pulling, like the Yoshinoya's "Large Atama", but if you overdo it, it will cause abdominal pain, so I think it's reasonable. If you order from the therapist, I think they will do it for a surcharge.