A Schedule II controlled substance is a category of drugs that have a high potential for abuse and can lead to severe psychological or physical dependence. These substances are regulated by the Controlled Substances Act in the United States and require a prescription from a licensed healthcare provider for legal use. Examples of Schedule II controlled substances include medications like morphine, oxycodone, and amphetamine. While they can be effective for treating certain medical conditions, their use is closely monitored to prevent misuse and addiction.