AbstractSince the 1970s, acupuncture has grown in popularity in industrialized countries. But still acupuncture remains a controversy among scientists. This literature study tries to elucidate some of the mechanisms proposed since acupuncture research took off about 30 years ago. Ever since acupuncturists started to practice in the western world, there has been an ongoing debate whether acupuncture is nothing more than a powerful placebo analgesia at best or whether there is a real mechanism behind the needle. This paper tries to explore the mechanisms behind the placebo effect in light of the new imaging techniques, fMRI. This tool enables us to visualize which area of the brain is activated during a placebo effect and during acupuncture. The results show that distinct areas of the brain are activated during each of the two modalities, but there is quite a lot of overlap. Based on current trials, the data are still inconclusive. The other known mechanism of acupuncture is its ability to stimulate the release of endogenous opioid peptides and mediate an analgesic effect. Subsequent research has proposed a consistent way to stimulate the release of particular endogenous opioid peptides using electro acupuncture at specific stimulation frequencies. Other proposed mechanisms for acupuncture are stress-induced-analgesia, local peripheral vasodilatation, and modulation of spinal cord receptor distribution through various mechanisms. A central issue in current acupuncture research is the lack of an adequate control measure, which contribute to the variable results seen and the often conflicting conclusions drawn from the same pool of research material. The data presented do not favor any one particular mechanism, but indicate that acupuncture is a multi-variable treatment modality. Whatever the outcome of this debate, both sides will make invaluable contributions to our knowledge of acupuncture.