A prescription drug is a medication that can be purchased or given out only with written instructions from a licensed healthcare provider, such as a doctor, dentist, nurse practitioner or physician’s assistant, to a pharmacist. These written instructions are known as a prescription.
I llegal drugs are illegal due to their unlicensed production, distribution, and possession. These drugs are also called "controlled substances". Most governments have designed legislation to criminalise illegal drug use. Even for simple possession, legal punishment can be quite severe (including the death penalty in some countries).