D. All of the above
All of the substances listed are classified as depressants:
A. Alcohol: It is a central nervous system depressant that slows down brain function and alters mood, cognition, and behavior.
B. Barbiturates: These are sedative-hypnotic drugs that depress the central nervous system, leading to relaxation, sedation, and reduced anxiety. They were once commonly prescribed for anxiety and sleep disorders but have been largely replaced by benzodiazepines due to their lower risk of overdose.
C. Benzodiazepines: These drugs, such as Valium and Xanax, are commonly prescribed for anxiety, insomnia, and muscle relaxation. They work by enhancing the effect of the neurotransmitter gamma-aminobutyric acid (GABA), which slows down brain activity and produces a calming effect.