RX stands for:
-the symbol that originated in medical prescriptions, (also written as "Rx") and "medical prescription" are sometimes used interchangeably. The use of Rx in prescriptions originated as an astrological symbol that was written for talismanic reasons at the start of medical prescriptions. Later it changed into Rx (an uppercase R with its tail crossed), and was used as an abbreviation for the Latin word recipe = "take" (imperative), i.e. an instruction to the pharmacist to take the items listed in order to prepare the medicine. When printing came, it was rendered as "Rx"
OR
-Rx or legend drug is a legal description in the United States for drugs that are only available on prescription from a licensed medical practitioner but are not controlled substances.

The word "prescription" can be decomposed into "pre" and "script" and literally means, "to write before" a drug can be prepared. Those within the industry will often call prescriptions simply "scripts".

Medical prescription

Both pharmacists and physicians are regulated professions in most jurisdictions. A prescription as a communications mechanism between them is also regulated and is a legal document.

Many brand name drugs have less expensive generic drug substitutes that are chemically equivalent. Prescriptions will also contain instructions on whether the prescriber will allow the pharmacist to substitute a generic version of the drug.

Some prescribers further inform the patient and pharmacist by providing the indicator for the medication; i.e. what is being treated. This assists the pharmacist in checking for errors as many common medications can be used for multiple medical conditions.

Some prescriptions will specify whether and how many "repeats" or "refills" are allowed; that is whether the patient may obtain more of the same medication without getting a new prescription from the doctor. Regulations may restrict some types of drugs from being refilled.

When filled by the pharmacist, prescriptions are typically assigned a "prescription number" (often abbreviated "Rx#") that is unique to the pharmacy that filled the prescription. The prescription number has the practical purpose of uniquely identifying the prescription later on while filed (both manual and electronic). The prescription number is also put on the label on the dispensed medication. The patient may be required to reference the prescription number for refills and drug insurance claims. There may also be a legal requirement for prescription numbers for subsequent identification purposes.

Related usage of the term prescription

Prescription may also be used as a short form for prescription drugs to distinguish from over-the-counter drugs. It may also be used in reference to the entire system of controlling drug distribution (as opposed to non-legal drugs). "Prescription" is often used as a metaphor for healthy directions from authority. A "green prescription" is direction from a doctor to a patient for exercise and healthy diet.

Prescription drug

A prescription drug is a licensed medicine that is regulated by legislation to require a prescription before it can be obtained. The term is used to distinguish it from over the counter drugs which can be obtained without a prescription. Different jurisdictions have different definitions of what constitutes a prescription drug. As a general rule, over the counter drugs are used to treat conditions not necessarily requiring a doctor's care and will have been proven to meet higher safety standards for self-medication by patients.

In the United States, the term "prescription drug" is most commonly used, but they are also called legend drugs or Rx-only drugs, after the requirements of Federal and state laws that all such drugs bear a "legend" prohibiting sale without a prescription; though more complex legends have been used, on most original drug packaging today the legend simply says "Rx only".