Acupuncture is a form of traditional Chinese medicine that has been practiced for centuries. It's based on the theory that energy, called chi, flows through and around your body along pathways called meridians. Acupuncturists believe that illness occurs when something blocks or unbalances your chi. Acupuncture is a way to unblock or influence chi and help it flow back into balance. Acupuncture is done by putting very thin needles into your skin at certain points on your body. This is done to influence the energy flow. Sometimes heat, pressure, or mild electrical current is used along with needles. Surprisingly, although needles are used, treatments are relatively pain-free. Results from a number of studies suggest that acupuncture may help ease types of pain that are often chronic such as low-back pain, neck pain, and osteoarthritis/knee pain. It also may help reduce the frequency of tension headaches and prevent migraine headaches. The effects of acupuncture on the brain and body, and how best to measure them, are only beginning to be understood. Current evidence suggests that many factors—like expectation and belief—that are unrelated to acupuncture needling may play important roles in the beneficial effects of acupuncture on pain.