The term 'lethargy inducer' can be defined as something that causes lethargy or drowsiness. Two crossword solutions for this term are OPIATE and NARCOTIC, both of which are drugs that can cause drowsiness and sedation. Opiates are derived from the opium poppy plant and include drugs such as morphine and codeine. Narcotics are a broader class of drugs that includes opiates, as well as synthetic drugs such as fentanyl. Both opiates and narcotics can be used to induce lethargy in medical settings, but they can also be abused and lead to addiction.