Heroin addiction is a dangerous addiction for a number of reasons. Namely, how the disease progresses. With continued use over time, the euphoric high becomes less and less powerful. As they chase this high, it gets worse and worse. Eventually, the addiction becomes so progressed that the main motivation for getting high is to avoid the onset of severe withdrawal symptoms. This is when heroin addiction stops being fun or exciting, and the nightmare begins and intensifies each time the last dose of heroin wears off.
The chemical composition of heroin is toxic and causes long term health effects. Harmful effects include permanent damage to blood vessels, the brain, lungs, kidney and liver. It can also cause long term damage to the brain, leading to memory loss and decreased cognitive function.
The effects of heroin use are not strictly health-related. In the drawls of addiction, the user often puts stress on their relationships, careers, and overall day to day life. Getting their next fix becomes more important than anything else in their life, including eating and bathing. They may not be aware of the damage that they are causing along the way, and even if they are, they may not be able to stop using without the proper addiction treatment.