For a communication to be accepted as a legal medical prescription, it needs to be filed by a qualified dentist, advanced practice nurse, physician, or veterinarian, for whom the medication prescribed is within their scope of practice to prescribe. This is regardless of whether the prescription includes prescription drugs, controlled substances, or over-the-counter treatments.

Prescriptions may be entered into an electronic medical record system and transmitted electronically to a pharmacy. Alternatively, a prescription may be handwritten on preprinted prescription forms that have been assembled into pads, or printed onto similar forms using a computer printer or even on plain paper, according to the circumstances. In some cases, a prescription may be transmitted orally by telephone from the physician to the pharmacist. The content of a prescription includes the name and address of the prescribing provider and any other legal requirements, such as a registration number (e.g., a DEA number in the United States). Unique to each prescription is the name of the patient. In the United Kingdom and Ireland, the patient's name and address must also be recorded. Each prescription is dated, and some jurisdictions may place a time limit on the prescription. In the past, prescriptions contained instructions for the pharmacist to use for compounding the pharmaceutical product, but most prescriptions now specify pharmaceutical products that were manufactured and require little or no preparation by the pharmacist. Prescriptions also contain directions for the patient to follow when taking the drug. These directions are printed on the label of the pharmaceutical product.

The word prescription, from pre- ('before') and script ('writing, written'), refers to the fact that the prescription is an order that must be written down before a drug can be dispensed. Those within the industry will often call prescriptions simply "scripts".

Every prescription contains who prescribed the prescription, who the prescription is valid for, and what is prescribed. Some jurisdictions, drug types or patient groups require additional information as explained below.
Many brand name drugs have cheaper generic drug substitutes that are therapeutically and biochemically equivalent. Prescriptions will also contain instructions on whether the prescriber will allow the pharmacist to substitute a generic version of the drug. This instruction is communicated in a number of ways. In some jurisdictions, the preprinted prescription contains two signature lines: one line has "dispense as written" printed underneath; the other line has "substitution permitted" underneath. Some have a preprinted box "dispense as written" for the prescriber to check off (but this is easily checked off by anyone with access to the prescription). In other jurisdictions, the protocol is for the prescriber to handwrite one of the following phrases: "dispense as written", "DAW", "brand necessary", "do not substitute", "no substitution", "medically necessary", "do not interchange". In Britain's National Health Service, doctors are reminded that money spent on branded rather than generic drugs is consequently not available for more deserving cases.
In some jurisdictions, it may be a legal requirement to include the age of child on the prescription. For pediatric prescriptions some advise the inclusion of the age of the child if the patient is less than twelve and the age and months if less than five. (In general, including the age on the prescription is helpful.) Adding the weight of the child is also helpful.
Prescriptions in the US often have a "label" box. When checked, the pharmacist is instructed to label the medication and provide information about the prescription itself is given in addition to instructions on taking the medication. Otherwise, the patient is simply given the instructions. Some prescribers further inform the patient and pharmacist by providing the indication 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 medical practitioner. Regulations may restrict some types of drugs from being refilled.

National or local (e.g. US state or Canadian provincial) legislation governs who can write a prescription. In the United States, physicians (either M.D., D.O. or D.P.M. ) have the broadest prescriptive authority. All 50 US states and the District of Columbia allow licensed certified Physician Assistants (PAs) prescription authority (with some states, limitations exist to controlled substances). All 50 US states and the District of Columbia, Puerto Rico and Guam allow registered certified nurse practitioners and other advanced practice registered nurses (such as certified nurse-midwives) prescription power (with some states including limitations to controlled substances). Many other healthcare professions also have prescriptive authority related to their area of practice. Veterinarians and dentists have prescribing power in all 50 US states and the District of Columbia. Clinical pharmacists are allowed to prescribe in some US states through the use of a drug formulary or collaboration agreements. Florida pharmacists can write prescriptions for a limited set of drugs. In all US states, optometrists prescribe medications to treat certain eye diseases, and also issue spectacle and contact lens prescriptions for corrective eyewear. Several US states have passed RxP legislation, allowing clinical psychologists who are registered as medical psychologists and have also undergone specialized training in script-writing, to prescribe drugs to treat emotional and mental disorders.

In August 2013, legislative changes in the UK allowed physiotherapists and podiatrists to have independent prescribing rights for licensed medicines that are used to treat conditions within their own area of expertise and competence. In 2018 this was extended to paramedics.
Some jurisdictions allow certain physicians (sometimes a government official like the state Secretary of Health, sometimes physicians in local clinics or pharmacies ) to write "standing orders" that act like a prescription for everyone in the general public. These orders also provide a standard procedure for determining if administration is necessary and details of how it is to be performed safely. These are typically used to authorize certain people to perform preventive, low-risk, or emergency care that would be otherwise logistically cumbersome to authorize for individual patients, including vaccinations, prevention of cavities, birth control, treatment of infectious diseases, and reversal of drug overdoses.
Doctors' handwriting is a reference to the stereotypically illegible handwriting of some medical practitioners, which sometimes causes errors in dispensing. In the US, illegible handwriting has been indirectly responsible for at least 7,000 deaths annually.

There are several theories about the causes of this phenomenon. Some sources say the extreme amount of writing doctors employ during training and at work leads to bad handwriting, whereas others claim that doctors neglect proper handwriting due to medical documents being intended to be read solely by medical professionals, not patients. Others simply classify the handwriting of doctors as a handwriting style.

Some jurisdictions have legislatively required prescriptions to be legible—Florida specifies "legibly printed or typed" —and the Institute for Safe Medication Practices advocated the elimination of handwritten prescriptions altogether. T…

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