Dilaudid (hydromorphone) is an opioid pain medication. An opioid is sometimes called a narcotic. Dilaudid is used to treat moderate to severe pain. Dilaudid may also be prescribed and used for other purposes. Dilaudid can slow or stop your breathing, especially when you start using this medicine or whenever your dose is changed. Never use Dilaudid in larger amounts, or for longer than prescribed. Do not crush, break, or open an extended-release pill.