How does acupuncture work?

It is called the placebo effect. In trials that compared acupuncture with "sham" acupuncture, on the other hand, there was no clear evidence that the real therapy was more effective. There may be another localised effect that has been reported this effect depends on a chemical called adenosine, which typically surges in concentration after any stress or injury, inserting and rotating a needle causes an excessive surge for what is a minor injury. Adenosine works by docking at a protein called the adenosine A1 receptor, which has well established roles in suppressing pain and is found on neurons that transmit pain signals. Traditional explanation of "how acupuncture works" that include meridians or 'energy' pathways that supposedly flow through the body have no basis in reality and are pure superstition.

Scientists have proven that acupuncture affects some of the major systems of the body such as the cardio-vascular system (Heart and Lung), Digestive and Gastro-Intestinal, Respiratory, Urinary, Immune, Endocrine, Nervous and the Reproductive system. The musculo-skeletal system (bone, joints and muscles) has been shown to respond to TCM treatment extremely well. You’ll see below examples of how acupuncturists affect these systems. Extensive research in the US, China, Japan and Australia has shown that acupuncture directly influences the immune, hormonal and nervous. How it Works: It is believed that when the needles are slightly inserted into the skin this stimulates the body's natural chemicals of healing to concentrate on that part of the body. However, this is one of many western medical explanations of acupuncture, which often fail to explain all of acupuncture's effects. A traditional explanation of "how acupuncture works" includes an understanding of meridian theory; meridians are energy pathways that connect internal organs and the surface of the body, to form a complex network. By stimulating specific points on the body along these meridians, the functioning of the body, including internal organs, the endocrine and nervous systems, as well as emotions can be altered. Selection and location of these acupuncture points is based upon a variety of systems, often specific to the style of the acupuncturist.

It doesn't. How can you "know" something such as this when quite the opposite is the case, it's been shown to be nothing more than a placebo and scam

By far the most likely explanation is the placebo effect. Its certainly not meridians and Qi. Edit: And just because its a placebo doesn't mean its not effective, the placebo effect can be absolutely amazing. Unlike a lot of other critical thinkers on this site (nothing against them - the whole subject is dressed up in an incredible amount of woo) I do actually think acupuncture is at least partially effective in some limited applications, but I don't see any reason to call it anything other than it is, which is a complex placebo.

To date there are a number of hypotheses in medical science as to the possible mechanism of action for Acupuncture. This link decently describes those hypotheses: http://www.healthy.net/scr/article.aspx?Id=1817 A newer hypothesis as to the mechanism of action involves the Bonghan duct network, but a lot more research is needed to clarify how this network might be involved. Traditional Chinese Medicine (TCM) theory states that by stimulating combinations of meridian points on the body, a physiological effect is generated. We use traditional language, such as Qi, Yin and Yang, but there are analogues to the physiological descriptions of action in TCM and modern medicine. What is very clear is that a least 5 Cochrane reviews show acupuncture is an effective treatment, surpassing placebo, and matching or surpassing standard care, for such things as nausea from chemotherapy, low back pain and knee pain.(1) The American College of Physicians recommends acupuncture as a second line treatment for low back pain that does not respond to standard care.(2) The Osteoarthritis Research Society International (OARSI) also recommends acupuncture.(3)