Dangerous Medical Abbreviations

In the medical field, there is frequently a need for quick and efficient communication. Time is often of the essence when providing care to patients. Medical abbreviations are a form of shorthand that allow healthcare professionals to easily communicate with one another.

Unfortunately, abbreviations can lead to confusion for both medical professionals and patients, thereby introducing the potential for dangerous misunderstandings. This can lead to errors in prescribing or administering medication and other treatments.1

Medical abbreviations can be misunderstood because:

  • Abbreviations vary by medical institution
  • Letters and symbols may be misread, particularly when written by hand
  • The same abbreviation can apply to multiple terms
  • Patients may not know what an abbreviation means

Abbreviations Causing Medical Errors

In 2007, researchers evaluated medication errors submitted to the United States Pharmacopeia MEDMARX, a national medication error reporting program that tracks medication errors across a number of hospitals and health systems in the United States. The study identified 30,000 abbreviation-related errors submitted from 2004 through 2006, which accounted for 4.7% of all medication errors reported in that timeframe. Among this data set, the 10 most common abbreviations resulting in medication errors were:2

Abbreviation Intended meaning Error %*
QD once daily 43.1%
U units 13.1%
cc mL 12.6%
MSO4, MS morphine sulfate 9.7%
X.0 mg or .X mg X mg or 0.X mg 3.7%
HS at bedtime 3%
MgSO4, Mag, Mg magnesium sulfate 2.5%
sc or sq subcutaneous 2.1%
QOD every other day 1.7%
1/2 half 1.5%

*As a percentage of all evaluated abbreviation-related medical errors.

Examples of Misinterpreted Scripts

Several real-world examples of handwritten orders that caused or came close to causing medical errors:

"6u" was misread as "60" and the patient received 60 units of insulin.
Humulin regular "10u" was misread as "100".
".5" was initially misread as "15" due to lack of a leading zero.
"QD" appeared as "QID". The error was identified before dose administration.
"sub q" was misread as "neb" and the dose was administered by nebulizer.
Plendil "5 mg" PO daily was read as “15 mg” due to poor spacing.

Source: ISMP reports. Images modified by OpenMD for display clarity.

Do Not Use Lists

To address the issue of medical errors caused by abbreviations, several institutions have developed lists of abbreviations that should be explicitly avoided. Most notable among these are the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) Do Not Use List and the Institute for Safe Medical Practices (ISMP) List of Error-Prone Abbreviations.

The following table includes some of the most common error-prone abbreviations and symbols:

Abbreviation Intended meaning Mistaken for Use instead
U or u unit 0, 4, cc "unit"
IU international unit IV (intravenous), 10 "international unit" or "units"
l or ml liter or milliliter 1 "L" or "mL"
cc cubic centimeter U (units) "mL" or "milliliter"
Ng or ng nanogram mg (milligram) or nasogastric "nanogram" or "nanog"
µg microgram milligram "mcg" or "microgram"
Q.D., QD, q.d., qd once daily Mistaken for QID or QOD "daily"
Q.O.D., QOD, q.o.d., qod every other day Mistaken for for QD or QID "every other day"
HS or hs half strength or at bedtime Mistaken for each other "half strength" or "at bedtime"
TIW, t.i.w., tiw three times a week tid (three times a day) or biw (twice a week) "three times weekly"
@ at 2 "at"
+ plus or and 4 "and"
< less than L or liter "less than"
> greater than 7 "greater than"
x5d For 5 days 5 doses "for five days"
IN intranasal IM (intramuscular) or IV "NAS" or "intranasal"
SC, SQ, sq, or sub q subcutaneously SL (sublingual) or 5Q (5 every) "SUBQ" or "subcutaneously"
D/C or d/c discharge or discontinue Mistaken for each other "discharge" or "discontinue"
MS morphine sulfate or magnesium sulfate Mistaken for each other Full drug name
MSO4 morphine sulfate magnesium sulfate "morphine sulfate"
MgSO4 magnesium sulfate morphine sulfate "magnesium sulfate"

High risk dose formatting:

Expression Intended Meaning Mistaken for Use instead
Lack of leading zero (.5 mg) .5 mg 5 mg "0.5 mg"
Trailing zero (5.0 mg)* 5.0 mg 50 mg "5 mg"

*A trailing zero may be used when necessary to demonstrate the level of precision in a reported value such as a laboratory result.

Impact of Do Not Use Lists

Various studies have endeavored to estimate the frequency of error-prone abbreviations in medical orders. While the baseline frequency varied widely* by institution, all studies reported a significant decrease in the use of error-prone abbreviations following institutional education programs that included the distribution of Do Not Use lists.3-5 Regular reminders and administrative enforcement were found to be critical to achieving the lowest possible rates.6 For example, in one hospital, pharmacists were directed to not dispense drugs and nurses to not administer orders for prescriptions that included error-prone abbreviations.4

*Frequency of error-prone abbreviations in medical records: 7.8% pre-intervention to 3.3% post-intervention (Samaranayake et al. 2014); 8.4% (Dooley et al. 2010) ; 19.7% pre-intervention to 3.3% post-intervention (Abushaiqa et al. 2007); 29% (Garbutt et al. 2006) ; 31.8% pre-intervention to 18.7% post-intervention (Taylor et al. 2007). This broad range is accounted for by researchers examining records in different clinical settings and applying different lists of error-prone abbreviations. It is further explained by the growing awareness of error-prone abbreviations that has led to industry-wide declines in their use over time.


The safest way to use medical abbreviations is to use only those that are agreed upon by an institution. Some medical institutions publish a list of acceptable and unacceptable abbreviations that can be reviewed with all healthcare employees. Other institutions may solely stress that employees never use the abbreviations noted on the Joint Commission’s Do Not Use list or ISMP’s List of Error-Prone Abbreviations.

“Using abbreviations may save minutes, prohibiting abbreviations may save lives.”
Brunetti, et al. 2007

Healthcare institutions are responsible for educating employees about the dangers of certain medical abbreviations, circulating Do Not Use lists, and reinforcing the message with annual reminders. They should also consider developing an enforcement system to ensure compliance. Enforcement might include steps such as prohibiting hospital pharmacists from filling prescriptions that contain a dangerous abbreviation or sending periodic reports to department heads identifying staff members who violate the abbreviation policy.6

The use of electronic prescribing systems has dramatically reduced the frequency of abbreviation and decimal formatting errors.9,10 However, until these systems are more widely used, education programs are strongly encouraged. When in doubt, medical professionals should spell out complete words and phrases to avoid any potential misunderstandings.

Additional resources:


  1. Tariq RA, Sharma S. StatPearls: Inappropriate Medical Abbreviations. [Updated 2021 Aug 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan.
  2. Brunetti L, Santell JP, Hicks RW. The Impact of Abbreviations on Patient Safety. The Joint Commission Journal on Quality and Patient Safety. 2007;33(9):576–583. doi:10.1016/S1553-7250(07)33062-6
  3. Taylor SE, Chu MT, Haack LA, McGrath A, To T. An intervention to reduce the use of error-prone prescribing abbreviations in the emergency department. J Pharm Pract Res. 2015;7(3):214–216. doi:10.1002/j.2055-2335.2007.tb00747.x
  4. Samaranayake NR, Cheung DST, Lam MPS, Cheung TT, Chui WCM, Wong ICK, et al. The effectiveness of a do not use list and perceptions of healthcare professionals on error-prone abbreviations. Int J Clin Pharm. 2014;36(5):1000–1006. doi:10.1007/s11096-014-9987-9
  5. Abushaiqa ME, Zaran FK, Bach DS, Smolarek RT, Farber MS. Educational interventions to reduce use of unsafe abbreviations. Am J Health Syst Pharm. 2007;64(11):1170–1173. doi:10.2146/ajhp060173
  6. Traynor K. Enforcement outdoes education at eliminating unsafe abbreviations. Am J Health Syst Pharm. 2004;61(13):1314,1317,1322. doi:10.1093/ajhp/61.13.1314
  7. Dooley MJ, Wiseman M, Gu G. Prevalence of error-prone abbreviations used in medication prescribing for hospitalised patients: multi-hospital evaluation. Intern Med J. 2012;42(3):e19–22. doi:10.1111/j.1445-5994.2011.02697.x
  8. Garbutt J, Milligan PE, McNaughton C, Waterman BM, Dunagan WC, Fraser VJ. A practical approach to measure the quality of handwritten medication orders. J Patient Saf. 2008;1(4). doi:10.1097/01.jps.0000205738.45580.5a
  9. Cheung S, Hoi S., Fernandes O, Huh J., Kynicos S, Murphy L, et al. Audit on the use of dangerous abbreviations, symbols, and dose designations in paper compared to electronic medication orders: a multicenter study. Ann Pharmacother. 2018;52(4):332–337. Epub 2017 Nov 3. doi:10.1177/1060028017740140
  10. Devine EB, Hansen RN, Wilson-Norton JL, Lawless NM, Fisk AW, Blough DK, et al. The impact of computerized provider order entry on medication errors in a multispecialty group practice. J Am Med Inform Assoc. 2010;17(1):78–84. doi:10.1197/jamia.M3285

Published: November 2, 2022