In psychology, consciousness refers to the awareness of your internal activities like thinking, feeling, sensing, and perceiving.  Under natural circumstances, humans experience altered states of consciousness in the form of sleep. However, these states can also be achieved by taking psychoactive drugs. Some altered states of consciousness are hypnosis and meditation.

The effects of all psychoactive drugs occur through their interactions with our endogenous neurotransmitter systems. Drugs can act as agonists or antagonists of a given neurotransmitter system. While agonist facilitates the activity of a neurotransmitter system, antagonists impede neurotransmitter activity. There are three major categories of psychoactive drugs namely depressant, stimulants, and hallucinogens.

A depressant such as alcohol is a drug that tends to suppress central nervous system activity. Excess intake of alcohol results in a variety of changes to consciousness.  People who take alcohol excessively feel sedated. With excessive alcohol use, a person might experience a complete loss of consciousness and/or difficulty remembering events that occurred during a period of intoxication.

Stimulants are drugs that tend to increase overall levels of neural activity. Examples of stimulants are cocaine, amphetamines, nicotine, and caffeine. Repetitive use of these stimulants alters one’s consciousness by inducing feelings of anxiety, hallucinations, and paranoia, and modifies the normal brain functioning.  Persons may engage in compulsive use of these stimulants in a bid to reinstate normal levels of neurotransmitters, leading to addiction.

A hallucinogen is one of a class of drugs that results in profound alterations in sensory and perceptual experiences. The people who use hallucinogens such as marijuana, psilocybin, and mescaline experience vivid visual hallucinations. These drugs may cause hallucinations of body sensations and a skewed perception of the passage of time.

To conclude, states of consciousness can be altered by using drugs. Depressants, stimulants, and hallucinogens are categories of psychoactive drugs.  Hypnosis and meditation are examples of altered states of consciousness.