These viruses are mainly spread through blood-to-blood contact. This means injecting drug users can contract HIV or hepatitis through sharing drug paraphernalia such as needles.
HIV and Hepatitis C can be avoided by taking precautionary measures. There is a vaccination available to protect against Hepatitis B.
People with severe mental health problems often use drugs to make the symptoms of their mental illness and the side effects of medication easier to manage. Alternatively, misusing drugs can trigger mental illness in someone with a predisposition to that illness. This is called a dual diagnosis.