4 Categories of Psychoactive Substances


Did you know that psychoactive substances are grouped into at least 4 categories? They are referred to as “psychoactive’ from the word “psycho” that implies, “brain”. This is because these substances and drugs affect your brain and changes how you behave or perceive what is happening around you.Pychoactive Substances are dangerous because they are small and soluble and are therefore able to pass penetrate into your brain through the Blood- Brain –Barrier, (BBB). BBB is a thin membrane which protects our brain from dangerous substances.

Psychoactive substances (Drugs and substances), have been grouped into 4 classes based on how they affect the brain. However, some drugs and substances do not fit in any of the 4 classes. Some drugs cut across the 4 categories since depending on the amount taken; their effects on your brain can vary. Let us look at these four categories of psychoactive substances.

  1. Depressants

Depressants are also referred to as sedatives or downers. They depress (slow down) the activity of your brain or the Central Nervous System (CNS).In other words, the brain become less active. Common substances and drugs in this category include;

  • Alcohol,
  • Barbiturates,
  • Benzodiazepine,

When intoxicated with depressants (sedatives), common symptoms include feeling drowsy (sleepy), slowed CNS, confused and uncoordinated movements among other side effects. With alcohol, there is potential overdose which can cause   dangerous withdrawal and death.


  1. Stimulants

The 2nd category of drugs and substances are the stimulants. These ones increase activities  of  the CNS. Common stimulants include;

  • Cocaine
  • Amphetamine
  • Methamphetamine
  • Nicotine
  • Caffeine
  1. Opioids

Opioids/opiates are generally used as pain killers. They depress the brain, reducing pain and inducing sleep. Commonly abused opiods are;

  • Heroin
  • Morphine
  • Opium
  1. Hallucinogens

These drugs cause vivid sensory distortions, alter mood and thinking. Among the most commonly abused are;

  • LSD
  • Mescaline
  • Peyote
  • Ecstasy
  • Mushrooms-peyote

Some drugs do not fit neatly into a category since their effects on the brain varies according to the amount taken. When taken in larger doses, some of them can activate the brain so much such that their effects imitate stimulants and yet when in small doses, they decrease the brain’s activities. Drugs in this group include;

  • Cannabinoids ,(marijuana, hashish),when taken in high doses, these drugs can stimulate the brain while in low doses, they depress the brain
  • Khat (Miraa or Muguka)
  • Dissociative anesthetics phencyclidine (PCP),
  • Ketamine,(date rape drug)
  • Inhalants solvents, gases, nitrites
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