Psychoactive substances, also known as psychotropic drugs, are substances that change the way the brain functions, leading to altered perceptions, moods, thoughts, and behaviors. These substances can be found in various forms, including illegal drugs, prescription medications, alcohol, and tobacco. Some other synonyms for the term 'psychoactive substance' include mind-altering drugs, psychoactive drugs, psychoactive agents, and psychoactive chemicals. These substances are often used for recreational, medical, or therapeutic purposes but can also be addictive and pose significant health risks. Therefore, it's important to use these substances with caution and only under the guidance of a medical professional.