Substance-Related Disorders

Drugs are an integral part of everyday life for many individuals, whether the drugs are used for legitimate medical purposes or recreationally.

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:

  • Alcohol.
  • Antianxiety and sedative drugs.
  • Caffeine.
  • Cannabis (including marijuana and synthetic cannabinoids).
  • Hallucinogens (including LSD, phencyclidine, and psilocybin).
  • Inhalants (such as paint thinner and certain glues).
  • Opioids (including fentanyl, morphine, and oxycodone).
  • Stimulants (including amphetamines and cocaine).
  • Tobacco.
  • Other (including anabolic steroids and other commonly abused substances).

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 website.

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; and
    • Substance-induced mental disorders.
  • Substance use disorders generally involve behaviour patterns in which individuals continue to use a substance despite having problems caused by its use.

What is Addiction Liability?

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; and
  • The drug’s ability to induce tolerance and/or symptoms of withdrawal.


The terms “addiction,” “abuse,” and “dependence” have traditionally been used in regard to individuals 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, medical professionals 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 (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.

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