Public health definitions
Public health practitioners have attempted to look at substance use from a broader perspective than the individual, emphasizing the role of society, culture, and availability. Some health professionals choose to avoid the terms alcohol or drug "abuse" in favor of language they consider more objective, such as "substance and alcohol type problems" or "harmful/problematic use" of drugs. The Health Officers Council of
British Columbia — in their 2005 policy discussion paper, A Public Health Approach to Drug Control in Canada] — has adopted a public health model of psychoactive substance use that challenges the simplistic black-and-white construction of the binary (or complementary)
antonyms "use" vs. "abuse".
 This model explicitly recognizes a spectrum of use, ranging from beneficial use to
A 2010 study ranking various illegal and legal drugs based on statements by drug-harm experts. Alcohol was found to be the overall most dangerous drug.
'Drug abuse' is no longer a current medical diagnosis in either of the most used diagnostic tools in the world, the
American Psychiatric Association's
Diagnostic and Statistical Manual of Mental Disorders (DSM), and the
World Health Organization's
International Statistical Classification of Diseases (ICD).
 has been adopted by the DSM as a blanket term to include 10 separate classes of drugs, including alcohol; caffeine; cannabis; hallucinogens; inhalants; opioids; sedatives, hypnotics, and anxiolytics; stimulants; tobacco; and other substances.
 The ICD uses the term Harmful use to cover physical or psychological harm to the user from use.
Physical dependence, abuse of, and withdrawal from drugs and other miscellaneous substances is outlined in the DSM a:
When an individual persists in use of alcohol or other drugs despite problems related to use of the substance,
substance dependence may be diagnosed. Compulsive and repetitive use may result in tolerance to the effect of the drug and withdrawal symptoms when use is reduced or stopped.
However, other definitions differ; they may entail psychological or physical
 and may focus on treatment and prevention in terms of the social consequences of substance uses.
This diagram depicts the correlations among the usage of 18 legal and illegal drugs: alcohol, amphetamines, amyl nitrite, benzodiazepine, cannabis, chocolate, cocaine, caffeine, crack, ecstasy, heroin, ketamine, legal highs, LSD, methadone, magic mushrooms (MMushrooms), nicotine and volatile substance abuse (VSA). Usage is defined as having used the drug at least once during years 2005–2015. The colored links between drugs indicate the correlations with |r|>0.4
, where |r|
Pearson correlation coefficient
Philip Jenkins suggests that there are two issues with the term "drug abuse". First, what constitutes a "drug" is debatable. For instance,
GHB, a naturally occurring substance in the central nervous system is considered a drug, and is illegal in many countries, while
nicotine is not officially considered a drug in most countries.
Second, the word "abuse" implies a recognized standard of use for any substance. Drinking an occasional glass of wine is considered acceptable in most Western countries, while drinking several bottles is seen as an abuse. Strict temperance advocates, who may or may not be religiously motivated, would see drinking even one glass as an abuse. Some groups even condemn
caffeine use in any quantity. Similarly, adopting the view that any (recreational) use of
substituted amphetamines constitutes drug abuse implies a decision made that the substance is harmful, even in minute quantities.
 In the U.S., drugs have been legally classified into five categories, schedule I, II, III, IV, or V in the
Controlled Substances Act. The drugs are classified on their deemed potential for abuse. Usage of some drugs is strongly correlated.
 For example, the consumption of seven illicit drugs (amphetamines, cannabis, cocaine, ecstasy, legal highs, LSD, and magic mushrooms) is correlated and the
Pearson correlation coefficient r>0.4 in every pair of them; consumption of cannabis is strongly correlated (r>0.5) with usage of nicotine (tobacco), heroin is correlated with cocaine (r>0.4), methadone (r>0.45), and strongly correlated with crack (r>0.5)
Drug misuse is a term used commonly when
prescription medication with
stimulant properties are used for mood alteration or intoxication ignoring the fact that overdose of such medicines can sometimes have serious adverse effects. It sometimes involves
drug diversion from the individual for whom it was prescribed.
Prescription misuse has been defined differently and rather inconsistently based on status of drug prescription, the uses without a prescription, intentional use to achieve intoxicating effects, route of administration, co-ingestion with
alcohol, and the presence or absence of dependence symptoms.
 Chronic use of certain substances leads to a change in the central nervous system known as a 'tolerance' to the medicine such that more of the substance is needed in order to produce desired effects. With some substances, stopping or reducing use can cause withdrawal symptoms to occur,
 but this is highly dependent on the specific substance in question.
The rate of prescription drug use is fast overtaking illegal drug use in the United States. According to the National Institute of Drug Abuse, 7 million people were taking prescription drugs for nonmedical use in 2010. Among 12th graders, nonmedical prescription drug use is now second only to
 "Nearly 1 in 12 high school seniors reported nonmedical use of Vicodin; 1 in 20 reported such use of OxyContin."
 Both of these drugs contain
Avenues of obtaining prescription drugs for misuse are varied: sharing between family and friends, illegally buying medications at school or work, and often "
doctor shopping" to find multiple physicians to prescribe the same medication, without knowledge of other prescribers.
Increasingly, law enforcement is holding physicians responsible for prescribing controlled substances without fully establishing patient controls, such as a patient "drug contract." Concerned physicians are educating themselves on how to identify medication-seeking behavior in their patients, and are becoming familiar with "red flags" that would alert them to potential prescription drug abuse.