Final answer:
Depressants are drugs that slow down the central nervous system's function by decreasing neurotransmission levels, thus reducing arousal and causing sedative effects.
Step-by-step explanation:
The group of drugs that slow down the normal function of the central nervous system (CNS) are known as depressants. These substances work by decreasing neurotransmission levels within the brain, leading to reduced arousal or stimulation in various areas. Among the commonly known depressants are barbiturates and benzodiazepines, which act as agonists for the gamma-Aminobutyric acid (GABA) system, thus inducing a calming effect on the brain and are often prescribed for issues like anxiety and insomnia.