Opioid overdose is very dangerous due to the way these drugs affect the central nervous system, which controls the heart and respiratory system. As a depressant, opioids slow these essential functions down. If a person isn’t breathing enough and/or the heart isn’t able to pump enough blood to get a sufficient amount of oxygen to the brain, a condition called hypoxia can occur. This is simply a lack of oxygen to essential tissues, causing rapid cell death. 