1. adj,. pertaining to a substance that produces insensibility or stupor. 2. n, Narcotic drug. Narcotic analgesics, derived from opium or produced synthetically, alter perception of pain; induce euphoria, mood changes, mental clouding, and deep sleep; depress respiration and the cough reflex; constrict the pupils; and cause smooth muscle spasm, decreased peristalsis, emesis, and nausea. Opioid is now the preferred term.