Drugs are an integral part of everyday life for many people, whether the drugs are used for legitimate medical purposes or recreationally (see table Drugs with Medical and Recreational Uses Drugs With Medical and Recreational Uses 
).
Substance-related disorders can arise when drugs that directly activate the brain's reward system are taken for the feelings of pleasure they induce. The pleasurable sensations vary with the drug. The drugs are divided into 10 different classes based on the different effects they produce in the body:
Caffeine
Cannabis (including marijuana Marijuana Marijuana (cannabis) is a drug made from the plants Cannabis sativa and Cannabis indica that contain a psychoactive chemical called delta-9-tetrahydrocannabinol (THC). Marijuana... read more and synthetic cannabinoids Cannabinoids, Synthetic Cannabis is a term for marijuana. Tetrahydrocannabinol (THC) is the main active ingredient in marijuana. Synthetic cannabinoids are man-made drugs that are similar to THC. They are usually sprayed... read more )
Stimulants (including amphetamines Amphetamines Amphetamines are stimulant drugs that are used to treat certain medical conditions, but are also subject to abuse. Amphetamines increase alertness, enhance physical performance, and produce... read more and cocaine Cocaine Cocaine is an addictive stimulant drug made from leaves of the coca plant. Cocaine is a strong stimulant that increases alertness, causes euphoria, and makes people feel powerful. High doses... read more )
Other (including anabolic steroids Anabolic Steroids Anabolic steroids are synthetic (man-made) versions of testosterone that are used to increase muscle size. Anabolic steroids are hormones that promote muscle growth and increase strength and... read more and other commonly abused substances Other Commonly Abused Substances Recreational drug use typically involves mind-altering drugs, but it may involve drugs taken for other purposes, usually losing weight or enhancing athletic performance. Taking these drugs without... read more )
Substance-related disorders can develop whether or not a drug is legal, is socially acceptable, or has an accepted medical use (with or without a prescription). Details about specific drugs and their effects are discussed elsewhere in THE MANUAL.
Types of Substance-Related Disorders
Substance-related disorders are usually broken down into two groups:
Substance-induced disorders are problems caused by the direct effects of a drug and include
Intoxication
Withdrawal
Substance-induced mental disorders
Substance use disorders generally involve behavior patterns in which people continue to use a substance despite having problems caused by its use.
Drugs in the 10 classes vary in how likely they are to cause a substance use disorder. The likelihood is termed addiction liability and depends upon a combination of factors including
How the drug is used
How strongly the drug stimulates the brain's reward pathway
How quickly the drug works
The drug's ability to induce tolerance Intoxication and/or symptoms of withdrawal Withdrawal Substance-induced disorders are a type of substance-related disorder that involves problems caused by the direct effects of a substance. Substance-induced disorders include Intoxication Withdrawal... read more
Definitions
The terms "addiction," "abuse," and "dependence" have traditionally been used in regard to people with substance use disorders. However, those terms are all too loosely and variably defined to be very useful and also are often used judgmentally. Thus, doctors now prefer to use the more comprehensive and less negative term "substance use disorder."
In discussions about controlled substances and drug use, the term "narcotics" is often used. This term refers to drugs that cause loss of feeling, a sense of numbness, and drowsiness, specifically opioids Opioids Opioids are a class of drugs derived from the opium poppy (including synthetic variations) that are pain relievers with a high potential for misuse. Opioids are used to relieve pain, but they... read more (drugs that bind to opiate receptors on cells). However, the term "narcotics" is also used in a broader (and inaccurate) sense to include any drug that is illegal or used illegitimately.
Scheduled Drugs
The Comprehensive Drug Abuse Prevention and Control Act (Controlled Substances Act) was implemented in the United States in 1970 and modified over the years to regulate the manufacture and distribution of certain classes of drugs, or controlled substances (see table Some Examples of Controlled Substances Some Examples of Controlled Substances* ).
Controlled substances are divided into 5 schedules (or classes) based on their potential for abuse, how accepted they are for medical use, and how safe they are when used under medical supervision. Schedule I drugs are considered the most harmful and therefore have the tightest controls. Schedule V drugs are considered the least harmful and are widely available. State and federal schedules may differ (see also US Drug Enforcement Administration Drug Schedules).
More Information
The following are some English-language resources that may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
Drug Enforcement Administration (DEA) Diversion Control Division: Home page of the main US government agency responsible for oversight of legal and illegal use of controlled substances. Contains links to a variety of information, including specific drug information, regulations and requirements, and various forms and applications.
United States Drug Enforcement Administration (DEA), Drug Scheduling:This link leads to further detail on the examples of controlled substances mentioned in this section.
