Ok.... there s different signs for cocaine and heroin. The big problem though, is if it s serious YOU WON T BE AWAKE TO KNOW WHAT TO DO. The overdose makes someone unconscious seconds after injection. There are pens of the antidote to narcotics. These cannot be given by the person who is overdoseing so, having someone with you with the pen is the only relevant context for it. Cocaine causes heart problems. Often these are fatal arrhythmias and the person just falls over dead. Unless you have someone with very good resusitation skills and equipment. It s pretty well hopeless. There can be stroke or heart attack with cocaine that is not immediately deadly. Signs of heart attack would include chest pain, difficulty breathing, sweats. The quality control of drugs of abuse is quite poor. Overdoses occur with single intravenous doses depending on the purity. These would be strong reasons to never do them again. Suboxone has blockers in it that prevent fatal narcotic overdose, at the down side of giving withdrawal if you use it and heroin together. But not fatal withdrawal.