It usually takes a substantial amount of alcohol to kill someone. It does not take a large amount of heroin to cause death. Injecting a drug gives a greater rush and provides, in colloquial terms, a 'bigger bang for the buck' than smoking or snorting the drug. However, injecting heroin results in higher levels of dependence on the drug. Injectors use more often, and quickly develop a tolerance to their drug of choice, whether it be heroin, speed or whatever.
Many people have to use more of the drug and use it more often.
A large number of cannabis smokers also smoke tobacco, exposing their lungs to the effects of two harmful substances. The purity of the heroin available in Australia has increased dramatically over the past few years. It has definitely played a considerable role in the growing number of heroin overdoses in this country. However, the majority of fatal and non-fatal heroin overdoses involve a cocktail of heroin and other drugs. Combining these drugs with even modest amounts of heroin can cause an overdose.