There are three different types of drug use. Drug dependence, drug addiction, and drug overdose. While most people would merge these terms together, I believe they deserve their own definitions. With each term being a representation of their own unique part of the term ‘drug use’, you need to fully understand each term to fully comprehend the definition of ‘drug use’.

It is possible to be dependent on a drug without being addicted. People taking drugs to treat diseases and disorders, that might hinder their ability to function, can experience improvement of their condition thanks to that drug. Being dependent on a drug normally means taking a drug regularly and experiencing unpleasant symptoms if discontinued. Dependence differs from addiction because, while addiction is often characterized by a psychological need for a drug, dependence can often be the result of legal, long-term use of medicine.
However, sometimes the dependence on a drug is unhealthy and a treatment is necessary. Treatment for dependence depends on the drug being withdrawn and often includes administration of another drug, especially for substances that can be dangerous when abruptly stopped. Treatments usually include the initiation and then tapering of a medicine that has a similar action in the brain but a longer half-life.

Drug addiction has two components, Physical dependency and psychological dependency. The physical dependency part of addiction occurs when a drug has been used habitually and the body has become accustomed to its effects. The person must then continue to use the drug in order to feel normal, or its absence will trigger withdrawal symptoms. The psychological dependency part occurs when a drug has been used habitually and the mind has become emotionally reliant on its effects and does not feel capable of functioning without it. Its absence can produce intense cravings. An addicted person may have either component of addiction or both.
Drug addiction has occurred throughout history, however, improvement in drug access, advancement in biochemistry, and a rising level of clinical recommendations for drug usage have intensified this problem greatly in the twentieth century.
The term drug overdose describes the ingestion of a drug, or other harmful substance, in greater quantities then recommended or generally practiced. Although sometimes overdoses are caused intentionally to commit suicide or self-harm, many overdoses are accidental and are usually the result of either irresponsible behavior or misread labels. Some causes of overdoses include use of multiple drugs and use after a period of abstinence or unexpected purity of the drug being consumed.
Symptoms of overdose include exaggerated forms of normal actions, other effects due to chemical properties of the medication, and non-specific symptoms due to central nervous system irritation. And while they do not give separate figures for drug overdoses and other kings of accidental poisonings, the National Center for Health Statistics report that 19,250 people died of accidental poisoning in the United States in the year 2004.
So, as you can see, though these different states of drug use can be meshed into one definition, each term is very unique and deserves its own explanation of its mechanics and characteristics. Once each term gets what it deserves, we can gain a better understanding of each separate term and thus gain a better understanding of their merged result.