Opiates and neurotransmitters, can you tell me the connection?

Many connections: The body makes its own opioids - endorphins, enkephalins and other substances (like substance P) that are themselves neurotransmitters in the pain system, and plus they cause release of others, particularly dopamine as well, which causes the euphoria and sense of well-being. Morphine and related drugs, plus synthetics like methadone, act on the same receptors our own opioids act on, but more so.