Endorphins act on several areas the brain, particularly the hypothalamus and the limbic system.
These areas are associated with emotion and behavior and they contain the receptor sites that interact with this group of chemicals. Testing has shown that during exercise the pituitary increases its production of B-endorphin. This can lead to the reactions stated above and also produce a sense of euphoria similar to that produced by opiates. This is where the perception that people can become addicted to exercise stems from. More research will have to be done to understand this phenomenon fully and to determine its significance on behavior.