Difference Between Drug Dose and Dosage

People often use dose and dosage interchangeably, but these terms have different meanings. By adding the suffix -age to the base dose, we are implying a regulated amount. It can be compared to the difference between the words mile and mileage.

This article describes the difference between the two terms and provides a few examples of each.

Dose and Dosage Definitions

The American Medical Association (AMA) Manual of Style is the definitive guide on medical writing and style. It assigns dose and dosage specific meanings.

In other words, a dose is simply an amount of a medication you take at one specific time. The dosage is the dose, or amount of drug, plus when and how often to take it. A dosage guides how you take or give the medication that's been prescribed.

Units for Doses

According to the AMA, drug doses are expressed in metric mass units (for example, milligrams or milligrams per kilogram). Some drugs (such as insulin or heparin) may be prepared as mixtures. For that reason, they have no specific molecular weight and can't be described in mass units.

There are a few exceptions to know. Liquid medications for the eyes and ears are sometimes measured in drops. Some medications are measured in grains. And some medications are dispensed using apothecary system measurements like teaspoonfuls, ounces, or drams. These are rare.

A dosage will be expressed in the same units, but over a specific time period—for example, "500 milligrams every six hours" or "500 milligrams four times per day."

Using Tylenol as an Example

Different typesr of Tylenol (acetaminophen) come in different doses. Which type and which dose you choose depends on the condition being treated. The age of the person taking the medication can also make a difference, especially with babies and children.

Here are some different Tylenol dosages:

• For minor aches and pains, take two tablets of Regular Strength Tylenol (a dose is 325 milligrams per tablet) every four to six hours as needed. Do not take more than 10 tablets in 24 hours. If the pain lasts more than a day or two, see a doctor.
• For more severe aches and pains (like a bad headache), take two Extra Strength Tylenol caplets (500 milligrams per caplet) every six hours as needed. Do not take more than six caplets per day. If pain lasts for more than a day or two, see a doctor.
• For arthritis pain, take two Tylenol Arthritis Pain caplets (650 milligrams per caplet) every eight hours as needed. Do not take more than six caplets per day.

Summary

The words dose and dosage don't mean the same thing. A dose is an amount of medication you take at one time. Doses are usually measured in metric mass units such as milligrams. The dosage is a set of instructions for how to take the medication. It includes how much to take, when to take it, and how long to take it.