A prescription is a health-care program implemented by a physician or other qualified health care practitioner in the formof instructions that govern the plan of care for an individual patient. The term often refers to a health care provider's written authorization for a patient to purchase a prescription drug from a pharmacist. A prescription is a health-care program implemented by a physician or other qualified health care practitioner in the formof instructions that govern the plan of care for an individual patient. The term often refers to a health care provider's written authorization for a patient to purchase a prescription drug from a pharmacist.