Prescription Writing 101

Prescription writing is something that I used to worry so much about in my 3rd year of medical school. I probably killed a whole tree tearing up prescriptions that were wrong. Why did I worry so much about it? Prescription writing was not covered very well at my medical school. And with the amount of material that needs to be covered in those 4 years, I'm sure writing prescriptions is not that well covered at any medical school. Maybe that's one of the reasons there are so many medication errors in medicine. Look at some of these commonly quoted statistics:

  • Medication errors occur in approximately 1 in every 5 doses given in hospitals.
  • One error occurs per patient per day.
  • 1.3 million people are injured and approximately 7000 deaths occur each year in the U.S. from medication-related errors
  • Drug-related morbidity and mortality is estimated to cost $177 billion in the U.S.

While these are just estimates from various studies and statistical models, the numbers are staggering. If there are 800,000 physicians in the United States, each physician accounts for $221,250! Do you still wonder why malpractice insurance is so expensive?

Hopefully if you are reading this, you are interested in NOT making mistakes. Even though I don't think I caused any major harm to any of my patients with prescription errors, I wish that I had read something like this when I first started writing prescriptions when I was in my 3rd year of medical school.


A prescription is an order that is written by you, the physician (or medical student with signature by a physician) to tell the pharmacist what medication you want your patient to take. The basic format of a prescription includes the patient's name and another patient identifier, usually the date of birth. It also includes the meat of the prescription, which contains the medication and strength, the amount to be taken, the route by which it is to be taken and the frequency. Often times, for “as needed” medications, there is a symptom included for when it is to be taken. The prescriber also writes how much should be given, and how many refills. Once completed with a signature and any other physician identifiers like NPI number or DEA number, the prescription is taken to the pharmacist who interprets what is written and prepares the medication for the patient. Let's break it down.

Patient Identifiers

According to the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) national patient safety goals, at least two patient identifiers should be used in various clinical situations. While prescription writing is not specifically listed, medication administration is. I think prescription writing should be considered in this category as well. The two most common patient identifiers are full name and date of birth. These are the FIRST things to write on a prescription. This way you don't write a signed prescription without a patient name on it that accidentally falls out of your white coat and onto the floor in the cafeteria.


This is an easy one. This is the medication you want to prescribe. It generally does not matter if you write the generic or the brand name here, unless you specifically want to prescribe the brand name. Remember, if you do want the brand name, you specifically need to tell the pharmacist – “no generics.” There are several reasons why you would want to do this, but we won't get into that here. On the prescription pad, there is a small box which can be checked to indicate “brand name only” or “no generics”.


After you write the medication name, you need to tell the pharmacist the desired strength. Many, if not most, medications come in multiple strengths. You need to write which one you want. Often times, the exact strength you want is not available, so the pharmacist will substitute an appropriate alternative for you. For example, if you write prednisone (a corticosteroid) 50 mg, and the pharmacy only carries 10 mg tablets, the pharmacist will dispense the 10 mg tabs and adjust the amount the patient should take by a multiple of 5.


Using my previous example for prednisone, the original prescription was for 50 mg tabs. The prescriber would have written “prednisone 50 mg, one tab….” (I'll leave out the rest until we get there). The “one tab” is the amount of the specific medication and strength to take. Again using my previous example, the instructions would be rewritten “prednisone 10 mg, five tabs….” You can see that “one tab” was changed to “five”. Pharmacists make these changes all the time, often without any input needed from the physician.


Up until this point, we have been using plain English for the prescriptions. The route is the first opportunity we have to start using English or Latin abbreviations. A NOTE: it is often suggested that to help reduce the number of medication errors, prescription writing should be 100% English, with no Latin abbreviations. I will show you both and let you decide. There are several routes by which a medication can be taken: By Mouth (PO), Per Rectum (PR), Sublingually (SL), Intramuscularly (IM), Intravenously (IV), Subcutaneously (SQ)

As you can see, the abbreviations are either from Latin roots like PO – per os – or just common combination of letters from the English word. Unfortunately when you are in a hurry and scribbling these prescriptions, (there is a truth behind never being able to read a physician's hand writing) many of these abbreviations can look similar. For example, intranasal is often abbreviated “IN,” which, when you are in a hurry, can be mistaken for “IM” or “IV.” Check this out:

Common Route Abbreviations:

  • PO (by mouth)
  • PR (per rectum)
  • IM (intramuscular)
  • IV (intravenous)
  • ID (intradermal)
  • IN (intranasal)
  • TP (topical)
  • SL (sublingual)
  • BUCC (buccal)
  • IP (intraperitoneal)

The frequency is simply how often you want the prescription to be taken. This can be anywhere from once a day, once a night, twice a day or even once every other week. Many frequencies start with the letter “q.” Q if from the Latin word quaque which means once. So it used to be that if you wanted a medication to be taken once daily, you would write QD, for “once daily” (“d” is from “die,” the Latin word for day). However, to help reduce medication errors, QD and QOD (every other day) are on the JCAHO “do not use” list. Instead you need to write “daily” or “every other day.”

Common Frequencies Abbreviations:

  • daily (no abbreviation)
  • every other day (no abbreviation)
  • BID/b.i.d. (Twice a Day)
  • TID/ (Three Times a Day)
  • QID/q.i.d. (Four Times a Day)
  • QHS (Every Bedtime)
  • Q4h (Every 4 hours)
  • Q4-6h (Every 4 to 6 hours)
  • QWK (Every Week)
The “Why” Portion

Many prescriptions that you write will be for “as needed” medications. This is known as a “PRN” (from the Latin pro re nata, meaning as circumstances may require). For example, you may write for ibuprofen every 4 hours “as needed.” What is commonly missed is the “reason.” Why would it be needed? You need to add this to the prescription. You should write “PRN headache” or “PRN pain” so that the patient knows when to take it.

How Much

The “how much” instruction tells the pharmacist how many pills should be dispensed, or how many bottles, or how many inhalers. This number is typically written after “Disp #.” I highly recommend that you spell out the number after the # sign, though this is not required. For example: I would write “Disp #30 (thirty).” This prevents someone from tampering with the prescription and adding an extra 0 after 30, turning 30 into 300.


The last instruction on the prescription informs the pharmacist how many times the patient will be allowed to use the same exact prescription, i.e. how many refills are allowed. For example, let's take refills for oral contraceptives for women. A physician may prescribe 1 pack of an oral contraceptive with 11 refills, which would last the patient a full year. This is convenient for both the patient and physician for any medications that will be used long term.

Prescription Writing Examples:
Prescription Writing 101 - Example

This example is a common medication prescribed when people are leaving the hospital. It is one 100 mg tablet, taken at bedtime. The prescription is for 30 pills and no refills.

Prescription Writing 101 - Example 2

Zofran is a very popular anti-nausea medication used after surgery. You'll notice this script is missing the “amount.” IV medications are a little different in that the amount and strength are kind of mixed together. This is not always the case though. You also see that this is an “as needed” or “PRN” medication. When the patient complains of nausea, the nurse can give this medication because it has been prescribed.

Prescription Writing 101 - Example 3

This example shows a common way to write prescriptions for liquids, especially for children. Obviously “liquid” isn't the medication, but you get the idea. Liquids come in specific strengths per amount of liquid. Here, the strength is 10 mg per 5 mL. We only want to give 5 mg though, so the “amount” that we prescribe is only 2.5 mL per dose. It's given by mouth every 4 hours. We are dispensing “1 (one) bottle”. You could also just write “1 (one)” as the pharmacist would know what you meant.

To finish up, here is a list of the JCAHO “Do Not Use” List:

  • U or u (unit) – use “unit”
  • IU (International unit) – use “International Unit”
  • Q.D./QD/q.d./qd – use “daily”
  • Q.O.D./QOD/q.o.d./qod – use “every other day”
  • Trailing zeros (#.0 mg) – use # mg
  • Lack of leading zero (.#) – use 0.# mg
  • MS – use “morphine sulfate” or “magnesium sulfate”
  • MS04 and MgSO4 – use “morphine sulfate” or “magnesium sulfate”

Did we miss an example you are looking for?  Give us a comment below and let us know!

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