Godsmack originally was a slang word for very high grade and pure heroin, and a killing dose therof. Street heroin is classified numerically from 1-4. Heroin # 4 may be up to 80% pure. Heroin of this purity is usually lethal if injected uncut. It is said the last thing an addict sees before he dies is God, therefore, Godsmack. The word smack was an early slang for heroin, so a fatal overdose is referred to as Godsmack.