Which of the following terms describes a situation where a medication is taken without a prescription?

The term that accurately describes a situation where a medication is taken without a prescription is "over-the-counter." Over-the-counter (OTC) medications are those that can be purchased without a doctor's prescription. These drugs are deemed safe and effective for the general public to use for self-treatment of common ailments, and they are usually regulated by health authorities to ensure their safety. In the context of taking medication without a prescription, OTC drugs represent the legal option that consumers can access directly.

The other terms refer to different classifications of drugs. Prescription drugs are medications that require a doctor's authorization due to safety concerns and the need for monitoring of their use. Controlled substances are a subset of prescription drugs that are regulated more stringently due to their potential for abuse or addiction. Illicit drugs, on the other hand, are illegal substances not approved for medical use, often associated with a high potential for abuse and legal penalties for possession or use. Hence, "over-the-counter" is the correct answer for describing medications accessed and taken without a prescription.