Endorphins are neurotransmitters produced in the brain known as endogenous opioids and they can be found in the pituitary gland, in other parts of the brain, or distributed throughout the nervous system. They transmit electrical signals within the nervous system by interacting with opiate receptors in the brain. The action is similar to morphine and codeine, but without addiction or dependence. At least 20 types of endorphins have been found in humans. In response to pain and stress, they decrease feelings of pain and also lead to feelings of euphoria, modulate appetite, release sex hormones, and enhance the immune response. As a result, it makes people feel less pain and less stressed.
Many studies in animals and humans have demonstrated that acupuncture can cause multiple biological responses. Endorphins are released during acupuncture and that the analgesic effects of acupuncture are at least partially explained by their actions. That opioid antagonists such as naloxone reverse the analgesic effects of acupuncture further strengthens this hypothesis.
