what happens when you OD?
Heroin (like morphine, methadone etc.) slows down or even stops your breathing, which means less oxygen gets to your brain and you risk falling into unconsciousness and suffocating. With amphetamines (speed), you could have a very fast heart rate, but still have difficulty in breathing and lose consciousness. Ketamine and GHB also make your breathing slow or erratic and may lead to coma.
Whatever the cause, you may actually stop breathing and you need help to stay alive. If you do not breathe for three to five minutes, you will be left with some degree of brain damage or die. When you stop breathing , someone else needs to breathe for you. This is called 'mouth-to-mouth' resuscitation or EAR - Expired Air Resuscitation.