Substance abuse, or drug abuse is about using a drug in ways that harm the health of its consumer. Very often, substance abuse involves taking drugs that are illegal, or using a drug that is legal for something other than its intended purpose. The term also covers the case of someone taking too much of a drug on purpose; very often this is called overdose. Psychoactive drugs are often abused.
The people who perform substance abuse are often addicted. The drugs most often associated with this term include alcohol, amphetamines, barbiturates, benzodiazepines (particularly alprazolam, temazepam, diazepam and clonazepam), cocaine, methaqualone, and opioids. Since many of these substances are illegal, very often the consumers also have a problem with the law.
In many cases, the personality of people change, when they are under the influence of a drug. Sometimes, crimes are committed under the influence of drugs. In many cases, people behave in antisocial ways. It has been observed that people who abuse drugs over a longer time often change their personality as well.