Something that is soporific is sleep-inducing. Certain medicines, but also extreme coziness, can have a soporific effect.
In the 1680’s, soporific, which doubles as both adjective and noun, was formed from the French soporifique. That word, in turn, came from the Latin sopor “deep sleep.” Beloved Peter Rabbit author Beatrix Potter once noted that, “It is said that the effect of eating too much lettuce is 'soporific'."
n a drug that induces sleep
a soporific drug that produces an uncontrollable desire to sleep
sleeping capsule, sleeping draught, sleeping pill, sleeping tablet
a soporific drug in the form of a pill (or tablet or capsule)