Classification of drugs - WHO and its effects


In this article, I will look at the main classifications used to group drugs, including the classification proposed by the World Health Organization.

Table of contents

Drugs are those substances that modify the normal functioning of the nervous system and create addiction. Currently, drug use is considered a major health problem in the population.

However, not all drugs are the same or produce the same effects. What types of drugs are there? There are different types of drugs, grouped according to different classification criteria.

How are drugs classified? In this article: classification of drugs according to the WHO and their effects, I will delve into the main classifications used to group drugs, especially the classification proposed by the World Health Organization.

What are drugs

What is a drug? According to the World Health Organization (WHO), "a drug is any substance that, introduced into the body by any route of administration, produces an alteration of the natural functioning of the central nervous system (CNS) of the individual and is also capable of creating dependency, whether psychological, physical or both."

In addition, drugs or psychoactive substances are capable of modifying a person's consciousness, mood, and thinking.

Let's break down this definition of drugs given by the WHO:

  1. Drugs are substances, therefore, drug dependencies are addictions to a substance. However, there are other behavioral addictions, such as pathological gambling.
  2. They are all substances that affect the CNS and create dependency. These substances can be both natural and artificial, and also legal or illegal.
  3. They can be introduced into the body by any route of administration. That is, they can be ingested orally, they can be smoked, they can be injected to be introduced intravenously and they can also be "snorted" or inhaled through the nose.
  4. They alter the central nervous system, therefore, they can excite, they can calm down, can calm the pain or they can distort the perception of reality.
  5. They create dependency, that is, all drugs have the ability to generate dependency. Dependence is understood as the need to consume the drug and presents a series of symptoms that indicate that the person has lost control over the consumption of the substance and continues to consume it even though they are aware of its adverse consequences.

Drug classification

How are drugs classified? Drugs or psychoactive substances can be classified according to different parameters, such as, for example, according to their origin or provenance, their structure, due to their effects on behavior, due to their danger to health, or due to their social impact.

As we can see, there are different criteria for grouping drugs, but in this article, we will focus on the most accepted classification and other common classifications:

  • According to the effect produced by the substances in the central nervous system, the most appropriate classification according to the WHO.
  • According to the legality of producing, possessing, marketing, or consuming the substances.
  • According to the dangerousness of the substances, a popular classification.

Types of drugs according to legality

Classification of drugs is based on the criteria of the legality of the substances. Legality refers to the legislation of each country. In this way, we find two main types of drugs:

Legal drugs are those psychoactive substances that are allowed, that is, whose use is not penalized by law. The legality of drugs varies according to the laws of each country, in addition, the consumption of said substance may be legal but not its sale.

On the other hand, the legality of drugs does not correspond to their dangerousness. Although they are legal, the abuse of drugs is dangerous and harmful to health.

So much so, that in our society, the drugs that are consumed the most and cause the most health problems are, precisely, legal drugs such as tobacco and alcohol. Legal drugs are:

  • The booze. This is the drug that has the greatest social acceptance. In Spain, its consumption is only legal from 18 years of age.
  • The nicotine. Tobacco is one of the most consumed drugs. Here you can see the effect of nicotine on the nervous system. It generates dependency, which can be evaluated with the Fagerström Test.
  • The caffeine. Caffeine has effects on the nervous system, therefore, it can be considered a psychoactive substance. However, its effects are much less and its consumption in normal amounts is not dangerous. Caffeine is mainly found in coffee, but also in soft drinks.
  • Theobromine and theophylline. Like caffeine, they are not dangerous in normal amounts. They can be found in tea and chocolate.
  • The drugs. Mainly, psychopharmaceuticals, which alter the CNS. Among them are benzodiazepines and amphetamines (under medical prescription). The use of drugs is medicinal and must be used under medical supervision.

2. Illegal drugs

Illegal drugs are those psychoactive substances whose use is not permitted by the law of the country. It may be that own consumption is allowed in some circumstances, but the sale is penalized.

Illegal drugs are the rest of the drugs. Among the most consumed illegal drugs are:

  • marijuana. It is considered the most widely used illegal drug. It is obtained from the hemp plant called Cannabis Sativa. Its active ingredient is tetrahydrocannabinol. Here you can see the symptoms and treatment of marijuana addiction.
  • The hashish. It is obtained from the resin of the same plant and shares the same active ingredient.
  • The cocaine. This illegal drug is obtained from the leaves of the coca plant called Erythroxylum coca. In addition to consuming it, it is also illegal to both grow and sell it.
  • The MDMA. It is known as ecstasy and is illegal due to the dangers and serious health consequences associated with its use.
  • Amphetamines or speed. They are considered illegal when used without medical supervision for recreational purposes.
  • The heroine. It is illegal to manufacture, sell, and possess this substance. It was made illegal after observing its serious consequences.
  • Phencyclidine or PCP. Although it had been used for analgesic purposes, today, it is an illegal drug.
  • LSD or lysergic acid diethylamide. It had psychiatric use but was made illegal due to its hallucinogenic effects.
  • Ketamine. It was used for anesthetic purposes but was also outlawed for its hallucinogenic effects.
  • The popper or amyl nitrite. It is a vasodilator that was made illegal after being consumed for recreational purposes.
  • Hallucinogenic mushrooms. They contain psilocybin and psilocin and are illegal because they cause hallucinations.

Classification of drugs according to the effect on the CNS

Grouping substances according to their effect on the central nervous system are considered the most correct way to classify drugs.

This classification is proposed by the World Health Organization and separates psychoactive substances into depressants, stimulants, and disturbers.

The three types of drugs are explained below:

1. Depressant drugs

Depressant drugs are substances that decrease the activity of the CNS. They do this by repressing the presynaptic structures, reducing the number of neurotransmitters, also reducing the function of the postsynaptic receptors.

The main groups of CNS depressant substances are:

  • sedatives/hypnotics
  • opiates
  • neuroleptics

Some examples of depressant drugs are:

2. Stimulant drugs

Stimulant drugs are substances that stimulate the activity of the CNS. They do this by blocking inhibition or by exciting neurons directly.

The stimulation is explained by the increase in neuronal depolarization, the increase in the number of neurotransmitters (NT) available, the lengthening of the action of NT, the weakness of the neuronal membrane, and the decrease in synaptic recovery time.

In this way, they can cause symptoms such as tachycardia, pupil dilation, sweating, increased blood pressure, etc. They may also be called sympathomimetics.

Stimulant drugs are the following:

  • amphetamines
  • cocaine
  • The caffeine
  • Theobromine and Theophylline
  • nicotine

3. The disturbing drugs

CNS disruptive drugs are those substances capable of modifying psychic activity and producing alterations in perception such as hallucinations, as well as altering mood and thought processes.

Some examples of disruptive drugs are:

  • LSD
  • hallucinogens
  • Cannabis
  • MDMA
  • Ketamine

There is a popular and colloquial way of classifying drugs into two types: hard or soft. This classification is made according to their perception of danger and social and health impact.

However, this classification is not considered adequate since it misleads by underestimating the risk of alcohol, tobacco, and cannabis.

1. Soft drugs

Drugs considered soft are those that are more socially accepted since they are perceived as less harmful. Something totally wrong, as I have already mentioned before, tobacco and alcohol are the drugs that carry the most health and human costs.

Although some soft drugs do not produce physical dependence, they do produce psychological addiction. 

Soft drugs are considered to be:

  • tobacco
  • alcohol
  • marijuana
  • hashish
  • anabolic steroids
  • The caffeine
  • the popper

2. Hard drugs

Drugs considered hard are perceived as having a greater social and health impact, given that their consumption is more dangerous in the short term.

These types of drugs correspond:

  • psychoactive drugs
  • the heroine
  • morphine
  • cocaine
  • amphetamines
  • MDMA or ecstasy
  • LSD
  • hallucinogenic mushrooms
  • the PCP
  • Ketamine
  • barbiturates
  • methadone

Types of drugs according to psychoanalytic models

Following this criterion, the following types of drugs were proposed :

  • Alcohol and barbiturates.
  • Amphetamines.
  • Cannabis (marijuana, hashish).
  • Cocaine.
  • Hallucinogens (LSD and the like).
  • opiates
  • Volatile solvents (glues, industrial products)
  • Tobacco.

In the models of higher rates of rehabilitation and maintenance of abstinence from drugs and alcohol, psychoanalytic positions are not used and the classic positions of S. Freud and J. Lacan are not included because they are systems of prolonged psychotherapy, which do not have the psychological goal of changing behavior or eliminating a habit or addiction, thus further limiting effectiveness.

The complication of psychoanalytic treatment means that in dealing with cocaine addiction, specialists use creativity and improvisation in many situations to try to provide help to the patient.

The results achieved by psychodynamic currents have been unfortunate, their theory and methodology are not configured for the treatment of human alterations and disorders of these characteristics.

During the psychotherapeutic approach of a drug addict or abuser, the first objective is the necessary urgency that exists to stop the consumption of the substance, this is the priority because while the subject consumes any drug or cocaine, his health and that of others are at risk.

It is very useful and urgent to guide and work with the presence of the person because it will be the only thing that he can handle and modify, for example, with the techniques of cognitive-behavioral therapy.

Drug effects

Drugs are chemical substances. When they are consumed, they reach the bloodstream and from there they travel throughout the body, including the brain.

When they reach the brain, drugs can produce different effects. As we have seen in the previous sections, we can differentiate between three types of effects of drugs on the brain or CNS: they can stimulate, they can relax or they can alter the senses.

  • The effect of stimulant drugs is to produce a feeling of being awake or having high energy, as well as euphoria, disinhibition, lack of emotional control, aggressiveness, lack of tiredness, psychomotor arousal, and irritability.
  • The effect of depressant drugs is sedative, therefore, they affect by reducing the perception of stimuli, relaxing, and providing a feeling of well-being and tranquility.
  • The effect of disturbing or hallucinogenic drugs are distortions in perception, and alteration of mood and thought. They cause the alteration of the senses in such a way that unreal sensations can be had.

Bottom line

There are many types of drugs and each drug produces its specific effect. Broadly speaking, we can say that most drugs cause drug addiction, although this is not the only danger.

Drug addiction has many consequences. Drugs negatively affect the ability to make decisions, which causes risky behaviors under their influence.

In general, drugs can cause illness, mental problems, family, social, legal problems, and even death. This is why it is so important to prevent drug addiction.

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  • World Health Organization (2004): Neuroscience of Psychoactive Substance Use and Dependence.
  • Berruecos Villalobos, L. (2010). Drug addiction, pharmacodependence and drug dependence: definitions, confusions and clarifications . Cuicuilco, 17(49), 61-81.
  • Hourmilougue, MC (1997). What is a drug?
  • Kramer, JF, Cameron, DC, & World Health Organization. (1975). Handbook on drug dependence: a compilation based on WHO expert group reports and other WHO publications.
  • Maturana, A. (2011). Alcohol and drug use in adolescents. Clinical Medical Journal Las Condes, 22(1), 98-109.
Disclaimer: This article is purely informative, I have no authority to make a diagnosis or recommend treatment. I invite you to visit a psychologist to treat your particular case.