Overview of Abbreviations on Prescriptions

Interpreting Your Confusing Medication Prescriptions

When your healthcare provider hands you a prescription for a medication, you may think some of it is written in another language—maybe because of its bad handwriting and/or perplexing abbreviations and symbols.

Doctor writing perscription
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Common Prescription Abbreviations 

Many abbreviations on a prescription pertain to how often a person should take a medication, like before a meal, or the route of administration, like inhaled versus by mouth.

Common Abbreviations
 Abbreviation  Meaning
a.c. or ac Before meals
b.i.d or bid Twice daily
h.s. or hs At bedtime
inh inhaled (like an asthma rescue inhaler)
p.c. or pc After meals
po By mouth (per oral)
p.r.n. or prn As needed
SC or SQ Subcutaneous (like an insulin injection)
s.o.s. or sos If necessary
t.i.d or tid Three times daily

The problem with medical abbreviations is that they can be misread or misunderstood by pharmacists, leading to a medication error, and this can be harmful to a patient. Bad handwriting is common, and a slip of the finger on an electronic prescription is also not far-fetched.

Banned Medical Abbreviations

 To prevent these medical errors, the Joint Commission on Accreditation of Hospitals (JCAH) created a "Do Not Use" list of abbreviations in 2003.

According to JCAH, for the following abbreviations, healthcare providers must write the full word and not the abbreviation on any order or medication-related document that is handwritten (including computer forms where there is free text) or pre-printed forms.

JCAH Do Not Use List
 Abbreviation  Meaning Problem Use Instead
IU International unit Can be mistaken for IV or the number 10 Write "International Unit"
Lack of leading zero (such as .5 mg) The decimal point may be missed, resulting in an overdosage Write 0.X mg
MgSO4, MS, MSO4 Magnesium sulfate or morphine sulfate Can be confused with each other Must write out either morphine sulfate or magnesium sulfate
Q.D, QD, q.d., qd Daily Can be mistaken for QOD Write "daily"
Q.O.D., QOD, q.o.d., qod Every other day The period after the Q and the O can be mistaken for "I" Write "every other day"
Trailing zero (such as 1.0 mg) The decimal point may be missed, resulting in overdosage Write X mg
 U or u Unit Can be mistaken for 0, 4. or cc Write "unit"

More Error-Prone Abbreviations

In 2005, the Institute of Medical Practices, or ISMP, also created a list of medical abbreviations that can cause errors. This list is much larger that the JCAHO list. Below are just a few examples.

Example of ISMP Error-Prone Abbreviations
 Abbreviation Meaning Problem Use Instead
cc cubic centimeters Can be mistaken for U (units) Write milliters or mL
μg micrograms Can be mistaken form mg (milligrams) resulting in an overdosage Write out micrograms or use mcg
SC or SQ  subcutaneous SC can be mistake for SL (sublingual) and SQ can be mistaken for "5 every" Write out subcutaneous or use subcut
 @ at Can be confused with the number 2 Write out at
 & and Can be confused with the number 2 Write out and

Bottom Line

In good practice, your healthcare provider should write out medical instructions fully on a prescription, including the medication name, frequency of intake, and route of administration—like ciprofloxacin 250 mg by mouth once daily. This ensures clear communication to the pharmacist and/or nurse and optimizes safety for you as a patient.

If you suspect an error on your prescription please notify your healthcare provider and pharmacist right away—even with the abbreviation guidelines, errors do occur. Trust your gut and your keen eye. You don't want to become a casualty of medical error.

Frequently Asked Questions

  • What does p.r.n. mean in medication?

    The abbreviation p.r.n. or prn on a prescription means as needed. It stands for the Latin phrase pro re nata, which translates to "as the circumstances arise."

  • What does b.i.d. mean on a prescription?

    Twice a day. B.i.d. or bid is an abbreviation for bis in die, a Latin phrase that translates to two times a day.

  • What does t.i.d. mean on a prescription?

    Three times a day. T.i.d. or tid is the abbreviation for ter in die, a Latin phrase that translates to three times a day.

  • What does SQ mean?

    SQ is a medical abbreviation for subcutaneous, meaning under the skin. It commonly refers to injections administered with a short needle to deliver medication to the fatty tissue under the skin. Insulin, for example, is given as a subcutaneous injection.

  • What does p.o. mean on a prescription?

    Oral route. P.o. or po on a prescription means the medication is taken by mouth. It is an abbreviation of the Latin term per os, which means by mouth. It is sometimes noted as per oral.


6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Dyasanoor S, Urooge A. Insight into quality of prescription writing - an instituitional studyJ Clin Diagn Res. 2016;10(3):ZC61–ZC64. doi:10.7860/JCDR/2016/18011.7472

  2. Weaver JM. It's time to throw out old-fashioned Latin abbreviationsAnesth Prog. 2006;53(1):1–2. doi:10.2344/0003-3006(2006)53[1:ITTTOO]2.0.CO;2

  3. Velo GP, Minuz P. Medication errors: prescribing faults and prescription errorsBr J Clin Pharmacol. 2009;67(6):624–628. doi:10.1111/j.1365-2125.2009.03425.x

  4. Sokol DK, Hettige S. Poor handwriting remains a significant problem in medicineJ R Soc Med. 2006;99(12):645–646. doi:10.1258/jrsm.99.12.645

  5. Thompson CA. JCAHO issues 'do-not-use' list of dangerous abbreviationsAm J Health Syst Pharm. 2003;60(24):2540–2542. doi:10.1093/ajhp/60.24.2540

  6. Institute for Safe Medication Practices. List of error-prone abbreviations. October 2, 2017.

Additional Reading
  • Glassman P. Making Health Care Safer II: An Updated Critical Analysis of the Evidence for Patient Safety Practices. Chapter 5. The Joint Commission's “Do Not Use” List: Brief Review (NEW). Rockville: Evidence Reports/Technology Assessments, No. 211, 2013. 
  • Kuhn, I.F. Abbreviations and acronyms in healthcare: when shorter isn't sweeter. Pediatric Nursing. 2007 Sep-Oct;33(5):392-8. 

By Colleen Doherty, MD
 Colleen Doherty, MD, is a board-certified internist living with multiple sclerosis.