sedative

nouns

a drug that reduces excitability and calms a person
depressant, downer, sedative, sedative drug

adjectives

tending to soothe or tranquilize
"valium has a tranquilizing effect"; "took a hot drink with sedative properties before going to bed"
ataractic, ataraxic, sedative, tranquilising, tranquilizing, tranquillising, tranquillizing
is derived from
sedate