Very fine stainless steel needles are inserted in acupuncture points located along channels(or meridians) and produce specific reactions in the related organ system. In acupuncture terms, the needle influences the flow or movement or qi and blood.
Research shows us that acupuncture increases endorphin output(which accounts for the relaxation patients feel during and after treatment) but clearly there are other mechanisms of action, not yet well understood, which bring about therapeutic benefit.
Sometimes leads are attached to the needles and a small electrical current is passed through them. The sensation may be barely perceptible but the needle is made to vibrate gently and stimulate the underlying blood vessels and tissues. The treatments designed to increase blood flow to the uterus and ovaries often use this approach.
Sometimes laser is used instead of an acupuncture needle. In this case it is the laser beam which stimulates the acupuncture point rather than a needle.