A medication is a substance used to treat or prevent disease. The word is broad. It includes prescription drugs, over-the-counter products, and supplements that make health claims. It includes pills, liquids, injections, patches, and inhalers. What unites them is purpose: they are taken to change a health outcome, whether that means lowering blood pressure, killing bacteria, or relieving pain.

Medications work in different ways. Some replace something the body is missing, like insulin or thyroid hormone. Some block a process that is causing harm, like a beta blocker slowing the heart. Some kill or inhibit foreign organisms, like antibiotics and antivirals. Some modify the immune system, like vaccines and biologics. The same medication can have different effects depending on the dose, the route, and the patient. Age, weight, kidney function, liver function, and genetics all influence how a person responds.

Safe medication use involves:

• Right drug. The correct medication for the condition.
• Right dose. The correct amount at the correct interval.
• Right route. The correct method of administration.
• Right time. The correct schedule.
• Right patient. The correct person.

These five rights are a cornerstone of nursing and pharmacy practice. Medication errors happen when one of them is missed.