Substance abuse is defined as a pattern of repeated use of substances such as alcohol, prescription medications, opioids, heroin, cocaine, methamphetamines, barbiturates, and other substances for the purpose of changing your mood. Over time, using substances can lead to changes in the way the brain functions as well as the structure of the brain itself, which can lead to numerous negative symptoms including addiction and dependence. If a person becomes dependent upon a drug, the use of the drug is not purely recreational – the person then requires the drug both physically and psychologically. Drug dependence and addiction are the reasons that an addict continues to abuse the substance even after they’ve experienced the negative health and emotional consequences.