That induces sleep; soporific, somniferous.
That accompanies falling asleep; especially, pertaining to the semi-conscious period immediately preceding sleep.
Inducing sleep; causing narcosis.
Of, or relating to narcotics.
Any substance or drug that reduces pain, induces sleep and may alter mood or behaviour; in some contexts, especially in reference to the opiates-and-opioids class, especially in reference to illegal drugs, and often both.
Any type of numbing or soothing drug.