Substance abuse by injection can be dangerous due to several reasons. When a person injects a drug, it bypasses the body’s natural defense mechanisms such as the digestive system and liver, and enters the bloodstream directly. This means that the drug can have a more powerful and immediate effect on the body and brain, which can increase the risk of overdose and other adverse health effects.

Injecting drugs can also increase the risk of contracting infections, such as HIV and hepatitis C, through the sharing of needles and other injection equipment. These infections can have serious long-term health consequences and can be life-threatening.

Furthermore, injection drug use can lead to the development of abscesses, infections, and other health problems at the injection site. These health issues can become chronic and require ongoing medical treatment.

In summary, injection drug use is dangerous due to the increased risk of overdose, infectious diseases, and other adverse health effects.