What is classified as a drug or substance that is illegal to possess or use unless specific legal conditions are met?

The correct choice identifies a controlled substance as a drug or substance that is illegal to possess or use unless specific legal conditions are met. Controlled substances are categorized by government regulations based on their potential for abuse, medical use, and safety. These may include drugs that are strictly regulated and require a prescription from a licensed healthcare provider for legal use, such as certain painkillers or stimulants.

This legal framework serves to prevent misuse and abuse, providing safeguards to ensure that substances with potential for addiction or harmful effects are used appropriately under medical supervision.

Other options, while related to various categories of medications and drugs, do not fit this specific legal context. Prescription medication is a category of controlled substances, but not all prescription medications are classified as controlled. Over-the-counter drugs are available without a prescription and do not fall under the same regulations. Recreational drugs can include both legal and illegal substances used for fun or enjoyment but do not necessarily imply a regulatory status concerning medical use.