The term DROWSINESS-INDUCING DRUG can be solved by the crossword solution OPIATE, which is a six letter word. An OPIATE is a type of drug derived from the opium poppy plant, and is known for its sedative and pain-relieving effects. Opiates are commonly used to treat pain, but can also be abused due to their highly addictive nature. When taken in large doses, opiates can cause drowsiness and even lead to overdose.