Acupuncture has won favor from the American people because it is safe.  For example, since 1972 there have been only 6 acupuncture accidents.  Many people have tried acupuncture therapy, but not everyone is convinced of its effect.  They are eager to know its mechanism, though it needs further explorations.  However, two theories have unraveled its profound mystery to some extent.  The first one is that mild pain relieves severe pain, and the other is about the study of opioid substances.  It believes that acupuncture induces internal production of endorphine and  enkephalin, which partly interprets the acupuncture effect.