Prescriptions also direct the instructions the pharmacist must give to the patient as to the dosage and frequency of the medication.
Prescriptions are always written on a patient's chart, or on a prescription pad - stationary with the physician's name and contact information. Most such prescription pads now contain security features to prevent forgery or fakery of a prescription.
A prescription is required for any medication that is designated a controlled substance and should not be taken without the direction of a physician. This can range from a simple antibiotic like penicillin to a powerful narcotic like Vicodin.
In addition, physicians prescribing narcotics must also have approval from the Food and Drug Administration. The FDA can remove the ability of a physician to prescribe these drugs on suspicion that a doctor is improperly prescribing them. Wilson had this permission withdrawn after he was under suspicion of writing improper Vicodin prescriptions to House, which left him effectively unable to carry on his practice.