What are the drug abbreviations?

October 11, 2025 •

4 min read

Studies have found that nearly 5% of all medication errors can be attributed to the use of abbreviations [1.4.2, 1.4.4]. So, what are the drug abbreviations and how can patients and providers decode them to ensure safety and prevent harm?

Quick Summary

A detailed look at common and dangerous medical abbreviations used for prescriptions. Learn to interpret dosage, frequency, and administration routes to improve medication safety and understand your treatment.

Key Points

High Risk for Errors: Nearly 5% of medication errors are linked to the use of abbreviations, making clarity in prescriptions crucial for patient safety [1.4.2, 1.4.4].
The 'Do Not Use' List: The Joint Commission maintains an official list of dangerous abbreviations (like 'U' for unit or 'Q.D.' for daily) that should never be used in medical communication [1.3.6].
Common Categories: Most abbreviations fall into categories describing frequency (BID, TID), route of administration (PO, IV), or dosage (mg, mL) [1.6.2].
Patient Vigilance is Key: Patients should always ask their doctor or pharmacist to clarify any abbreviation or instruction they do not understand to prevent mistakes [1.5.1].
Modern Solutions: Electronic Health Records (EHRs) and computerized order entry help reduce errors by standardizing prescriptions and flagging ambiguous terms [1.5.5].

The Language of Prescriptions: Why Are Abbreviations Used?

In healthcare, drug abbreviations are a form of shorthand used by medical professionals to communicate complex information quickly and efficiently [1.8.2]. Rooted largely in Latin, this practice developed to save time and space on handwritten charts and prescriptions [1.6.2, 1.7.4]. For example, instead of writing "take twice a day by mouth," a doctor could simply write "PO BID" [1.7.4]. This system was intended to streamline communication between doctors, pharmacists, and nurses. However, while efficient, the use of abbreviations introduces significant risks of misinterpretation, which can lead to dangerous medication errors [1.8.1]. In response, regulatory bodies and healthcare institutions have pushed for clearer communication, including the adoption of electronic health records (EHRs) and standardized "Do Not Use" lists to protect patient safety [1.3.1, 1.5.5].

Common Categories of Drug Abbreviations

Understanding a prescription requires familiarity with several categories of abbreviations. These shortcuts provide essential instructions for how a medication should be taken.

Frequency and Timing

These Latin-derived terms dictate how often and when to take a medication [1.6.1, 1.6.2]:

AC (ante cibum): Before meals
PC (post cibum): After meals
BID (bis in die): Twice a day
TID (ter in die): Three times a day
QID (quater in die): Four times a day
QD (quaque die): Every day (Note: This is often on 'Do Not Use' lists) [1.3.6]
HS (hora somni): At bedtime
PRN (pro re nata): As needed
STAT (statim): Immediately

Route of Administration

This indicates how the medication enters the body [1.7.2, 1.2.2]:

PO (per os): By mouth, orally
IV (intravenous): Into a vein
IM (intramuscular): Into a muscle
SC / SQ (subcutaneous): Under the skin
SL (sublingual): Under the tongue
OD (oculus dexter): Right eye
OS (oculus sinister): Left eye
AU (aures unitas): Both ears

Dosage and Measurement

These abbreviations specify the quantity of medication:

g: gram
mg: milligram
mcg: microgram (Note: 'μg' is often discouraged) [1.5.2]
mL: milliliter (Note: 'cc' is discouraged) [1.5.2]
gtt: drop [1.2.2]
tab: tablet [1.6.5]
cap: capsule [1.6.5]

The Dangers of Ambiguity: The "Do Not Use" List

Misinterpreting a single letter can have severe consequences. To combat this, The Joint Commission established an official "Do Not Use" list in 2004 as part of its National Patient Safety Goals [1.3.1, 1.3.5]. This list identifies abbreviations that are easily confused and have been linked to medication errors. For example, the abbreviation "U" for "unit" can be misread as a zero ("0") or the number four ("4"), potentially leading to a tenfold or greater overdose, especially with high-alert drugs like insulin [1.4.7, 1.8.1]. Similarly, "Q.D." (daily) has been mistaken for "Q.I.D." (four times a day) [1.5.2, 1.8.1]. Healthcare organizations are required to adhere to this list for all patient-related documentation to minimize risk and improve communication clarity [1.3.1].

Comparison Table: Safe vs. Dangerous Abbreviations


Intended Meaning	Dangerous Abbreviation	Recommended Practice
Unit	U, u	Write "unit" [1.3.6]
International Unit	IU	Write "International Unit" [1.3.6]
Daily	Q.D., QD, q.d., qd	Write "daily" [1.3.6]
Every Other Day	Q.O.D., QOD, q.o.d.	Write "every other day" [1.3.6]
Morphine Sulfate	MS	Write "morphine sulfate" [1.3.6]
Magnesium Sulfate	MSO4, MgSO4	Write "magnesium sulfate" [1.3.6]
Micrograms	µg	Write "mcg" [1.5.2]
Cubic Centimeters	cc	Write "mL" [1.5.2]
At Bedtime	HS	Write "at bedtime" or "half-strength" as intended [1.5.2]
Discharge / Discontinue	D/C	Write "discharge" or "discontinue" [1.5.2]

How Patients Can Ensure Medication Safety

As a patient, you are the final checkpoint in the medication process. Taking an active role is crucial for preventing errors.

Ask Questions: If you don't understand an abbreviation or any part of your prescription, ask your doctor or pharmacist to explain it. Never assume.
Request Clarity: Ask your doctor to write out instructions in full, avoiding abbreviations [1.5.1]. Many electronic prescribing systems do this automatically.
Use the Teach-Back Method: After receiving instructions, explain them back to your healthcare provider in your own words. For example, say, "Okay, so I will take one pill by mouth in the morning and one at night."
Keep an Updated List: Maintain a current list of all your medications, including prescription drugs, over-the-counter medicines, and supplements, and share it at every appointment [1.5.3].
Verify the Indication: Best practices encourage prescribers to include the medication's purpose (e.g., "for blood pressure") directly on the prescription to add another layer of safety [1.5.1]. Confirm this with your pharmacist.

Conclusion

Drug abbreviations are a double-edged sword in pharmacology. While created for efficiency, they carry inherent risks that can compromise patient safety. The shift towards electronic health records and the enforcement of "Do Not Use" lists by organizations like The Joint Commission are critical steps in mitigating these dangers [1.3.2, 1.5.6]. However, the most important safeguard is an informed and vigilant patient. By actively engaging with healthcare providers, asking for clarification, and understanding the potential pitfalls of medical shorthand, you can help ensure your treatment is both effective and safe.

For more information on prohibited abbreviations, you can visit The Joint Commission's resource page [1.3.2].

Frequently Asked Questions

PRN comes from the Latin phrase 'pro re nata' and means to take the medication 'as needed' for a specific symptom, such as pain or nausea [1.2.5, 1.6.2].

The abbreviation 'U' is on The Joint Commission's 'Do Not Use' list because it can be easily mistaken for the number '0' or '4', which can lead to a significant overdose, especially with drugs like insulin [1.3.6, 1.8.1].

BID (bis in die) means twice a day, while TID (ter in die) means three times a day. These Latin terms instruct you on the frequency of your medication doses [1.2.1, 1.6.1].

'PO' is the abbreviation for the Latin term 'per os,' which means 'by mouth' or 'orally.' It indicates that the medication should be swallowed [1.2.5].

While many doctors now use electronic systems that minimize abbreviation use, some may still use them. Best practices encourage writing out full terms to avoid confusion. If you see an abbreviation, it is always best to ask for clarification [1.5.1].

If any part of your prescription is illegible, ask your doctor to clarify it immediately. Your pharmacist will also verify the prescription, but asking upfront is the safest approach to prevent errors [1.5.1].

The official 'Do Not Use' list is maintained by The Joint Commission and is available on their website. It is part of their National Patient Safety Goals to improve communication in healthcare [1.3.2].