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Psychoactive substances

A psychoactive substance is defined as a chemical substance, other than a nutrient or essential dietary ingredient, that affects brain function to produce alterations in sensation, perception, mood, consciousness, cognition, and behaviour

Exposure to a psychoactive substance can cause changes in the structure and functioning of neurons.


Why people use psychoactive drugs

  • for pleasure - they like the feeling the drug gives 
  • because friends and family use them 
  • because they like the 'taste' 
  • to relieve tension and relax 
  • to be part of a religious or social ceremony 
  • because they are lonely, to relieve boredom 
  • for pain relief 
  • to help cope with problems and forget worries 
  • because they have grown dependent on the drug 
  • because they feel ill if they stop 
  • to do things that they usually could not or would not do - it gives them courage


Psychoactive substances, Definition

A psychoactive substance is defined as a chemical substance, other than a nutrient or essential dietary ingredient, that affects brain function to produce alterations in sensation, perception, mood, consciousness, cognition, and behaviour. According to the World Health Organization (Department of Mental Health and Substance Abuse, Management of Substance Abuse Team), “psychoactive substances are substances that, when taken in or administered into one's system, affect mental processes, e.g. cognition or affect. This term and its equivalent, psychotropic drug, are the most neutral and descriptive term for the whole class of substances, licit and illicit, of interest to drug policy. ‘Psychoactive’ does not necessarily imply dependence-producing, and in common parlance, the term is often left unstated, as in ‘drug use’ or ‘substance abuse’ “.


Commonly used psychoactive substances

Depressants : they slow down the central nervous system; for example: tranquillisers, alcohol, heroin and other opiates, cannabis

Stimulants : they excite the nervous system; for example: nicotine, amphetamines, cocaine, caffeine

Hallucinogens : they distort how things are perceived; for example: LSD, mescaline, 'magic mushrooms', cannabis


Index of psychoactive substances

Hallucinogens (Mushrooms, LSD, LSA, AL-LAD, DMT, 5-MeO-DMT, Harmine, Ibogaine, Mescaline, Salvia, Muscimol, 2C-X series, DOx series, NBOMe series. 

Depressants (Cannabis, Alcohol, GHB, Benzodiazepines, Opioids [Heroin, Codeine, Tramadol, Morphine, Opium, Hydrocodone, Hydromorphone, Oxycodone, Oxymorphone, Poppy extracts, Fentanyl]). 

Stimulants (Adderall, MDMA, Cocaine, Methamphetamine, Street amphetamine, Ephedrine, 5-APB, Nicotine)

Dissociatives (DXM, Ketamine, MXE, Nitrous, PCP, 

Deliriants (Diphenhydramine, Scopolamine) 


Legal Drug trade

Alcoholic beverages, containing psychoactive ethyl alcohol, are produced legally throughout the world. Their production supports a commercial alcohol industry. Consumption of alcohol is subject to regulation in most countries, namely by means of age restrictions. 

Tobacco, a recreational drug containing nicotine, is produced legally in countries such as Cuba, China, and the United States. This also supports a tobacco industry and the production of a variety of tobacco products, which, like alcoholic beverages, are subject to age restrictions in most countries. 

Caffeine, a stimulant drug, is extracted from plants including the coffee plant and the tea bush. It is the most widely consumed psychoactive substance in the world, remaining unregulated and generally recognized as safe by the U.S. Food and Drug Administration.


Effects in the brain

A drug can have psychological, emotional and physical effects and can change the behaviour of the person taking the drug. These behavioural changes are not the same for everyone. The effect of any drug will depend on (1) the drug: what effect it has on the central nervous system; the amount taken; how it is taken; how often; for how long; if it is taken with other drugs, (2) the person: age, weight, sex, tolerance, past experiences, mood, personality, the expectations and what the person wants to happen from using the drug, (3) the environment: what the community or society expects, allows and excuses as a result of using the drug; the place; the presence of other people; noise levels, and so forth. 

Exposure to a psychoactive substance can cause changes in the structure and functioning of neurons, as the nervous system tries to re-establish the homeostasis disrupted by the presence of the drug (see also, neuroplasticity). Exposure to antagonists for a particular neurotransmitter can increase the number of receptors for that neurotransmitter or the receptors themselves may become more responsive to neurotransmitters; this is called sensitization. Conversely, overstimulation of receptors for a particular neurotransmitter may cause a decrease in both number and sensitivity of these receptors, a process called desensitization or tolerance. Sensitization and desensitization are more likely to occur with long-term exposure, although they may occur after only a single exposure.



Abstinence: when people decide not to use a drug or to stop taking a drug or substance at all times and under all circumstances. 

Addiction, addictive behavior, drug dependence: the person (1) has a strong desire or compulsion to use the drug, (2) finds it difficult to control the drug using behavior, (3) is uncomfortable or distressed if the drug taking is prevented or stops (withdrawal symptoms), (4) keeps using the drug, even when it is causing problems 

Binge drinking: rapid consumption of alcohol over a short period of time to the point of intoxication. 

Detoxification: The process by which an individual is withdrawn from the effects of a pychoactive substance. 

Disease model of drug addiction: Addiction to drugs has been seen as a 'disease' that affects the whole person. If people have the 'disease' then they are more likely to become addicted to the drug. 

Drug abuse: Drug use that causes harm. 

Drug misuse: A harmful or inappropriate use of drugs. 

Drug dependence: When a drug becomes central to a person's thoughts, emotions and activities. 

Drug use: This term means taking drugs. The term does not necessarily mean that the drug taking is harmful or ongoing. 

Experimental use: Sometimes people try out a drug to see what it is like. They might try it once or a couple of times. Many children experiment with different drugs with their friends or family members. 

Harm minimisation/harm reduction: A drug strategy based on a harm minimisation approach and to prevent the initiation into harmful or hazardous drug use, especially by young people. 

Harm-reduction strategies: They are designed to reduce the impacts of drug-related harm on individuals and communities. 

Harmful use: This term describes drug use that causes damage to either mental or physical health. It can also refer to the harm caused to the drug user's family or community in general. 

Intoxication: When they use an amount of a substance that produces noticeable changes in their behaviour. 

Recreational or social use: Sometimes people use a drug or drugs on a casual basis to enhance socialising or to increase their enjoyment of leisure and recreational activities. 

Tolerance: The person's body adapts to the presence of the drug and the person has to increase his or her intake of the drug to get the desired effect, for example, to feel 'high'. 

Withdrawal: When a person stops taking the drug, he or she may experience certain unpleasant physical and mental effects.



Griffiths, RR , 1995. Psychopharmacology: The Fourth Generation of Progress, 4th ed.). Lippincott Williams & Wilkins. p. 2002.   Edwards, Griffith, 2005. Matters of Substance: Drugs—and Why Everyone's a User. Thomas Dunne Books. p. 352. 

WHO Regional Offices,

E.M.C.D.D.A. European Monitoring Centre for Drugs and Drug Addiction,

UNODC United Nations Office on Drugs and Crime (formerly UNDCP), 

Council of Europe's Pompidou Group,

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