Excitants are substances that stimulate or excite the nervous system. Antonyms of excitants can be sedatives or depressants, which are substances that slow down the nervous system. Sedatives like alcohol, benzodiazepines, and barbiturates are used to reduce anxiety, promote relaxation, and induce sleep. Depressants like opioids and opiates are used to relieve pain, suppress coughs, and induce anesthesia. These substances can be addictive and cause dependence, and their misuse can lead to serious health problems. Therefore, it is important to use them only as prescribed and under the guidance of a healthcare professional.