Decoding Your Prescription: What are the Abbreviations Used in Prescription?

October 11, 2025 •

4 min read

Nearly 5% of all medication errors are attributable to the use of abbreviations, underscoring the critical need for patients to understand what are the abbreviations used in prescription. This guide demystifies the shorthand on your prescription, from dosing frequency to administration routes, to help ensure proper medication use and safety.

Quick Summary

Prescription abbreviations, often derived from Latin, are medical shortcuts for dosage, frequency, and route of administration. Understanding this shorthand is crucial, as misinterpretation can lead to dangerous medication errors and compromise patient safety.

Key Points

Latin Roots: Many prescription abbreviations are derived from Latin phrases that concisely describe dosing frequency and route of administration.
Risk of Errors: The use of abbreviations, especially in handwritten prescriptions, can lead to serious medication errors due to potential for misinterpretation.
"Do Not Use" Lists: To enhance patient safety, many healthcare institutions and regulatory bodies mandate "Do Not Use" lists for high-risk abbreviations, such as 'QD' and 'U'.
E-Prescribing Improves Safety: Electronic prescribing reduces the risks associated with abbreviations by standardizing language and eliminating ambiguous handwriting.
Patient Empowerment: Understanding common abbreviations and always asking for clarification from a pharmacist or doctor is a crucial step for patients to ensure their medication is taken correctly.
Common Abbreviations: Essential abbreviations include b.i.d. (twice a day), t.i.d. (three times a day), q.i.d. (four times a day), p.r.n. (as needed), and p.o. (by mouth).

The Origins and Purpose of Prescription Abbreviations

The practice of using abbreviations on prescriptions dates back centuries, rooted in Latin phrases that were once the lingua franca of medicine. The original purpose was to provide a quick, efficient, and standardized way for medical practitioners to communicate complex instructions to pharmacists. These shortcuts saved time and minimized the space needed for documentation, which was particularly important in the era of handwritten notes and records. For instance, a directive like bis in die (twice a day) could be quickly and easily abbreviated to 'BID'. While the use of Latin has faded in everyday medical language, the abbreviations have persisted as a form of shorthand.

Today, despite the move towards electronic prescribing, these abbreviations are still a foundational part of pharmacology. However, their use presents a double-edged sword: they can expedite communication but also introduce significant risks if misinterpreted. Organizations like the Joint Commission and the Institute for Safe Medication Practices (ISMP) have identified several error-prone abbreviations and created "Do Not Use" lists to mitigate these risks.

Common Abbreviations for Medication Frequency and Timing

One of the most critical aspects of any prescription is the dosing schedule. Taking medication at the correct intervals is vital for managing chronic conditions, ensuring drug efficacy, and avoiding side effects. Here is a list of some of the most common frequency and timing abbreviations you might encounter:

a.c.: ante cibum, meaning 'before meals'.
p.c.: post cibum, meaning 'after meals'.
h.s.: hora somni, meaning 'at bedtime'.
q.h.: quaque hora, meaning 'every hour'.
b.i.d.: bis in die, meaning 'twice a day'.
t.i.d.: ter in die, meaning 'three times a day'.
q.i.d.: quater in die, meaning 'four times a day'.
q.d.: quaque die, meaning 'every day' (on "Do Not Use" lists due to confusion with 'QID').
q.o.d.: quaque [other] die, meaning 'every other day' (also on "Do Not Use" lists).
p.r.n.: pro re nata, meaning 'as needed'.

Abbreviations for Administration Routes and Dosage

In addition to the timing, a prescription must specify how the medication is to be administered. For a patient, understanding the correct route is just as important as the frequency.

p.o.: per os, meaning 'by mouth' or 'orally'.
i.m.: 'intramuscular', meaning injected into a muscle.
i.v.: 'intravenous', meaning injected into a vein.
subq: 'subcutaneous', meaning injected under the skin.
gtt: guttae, meaning 'drop'.
od: oculus dexter, meaning 'right eye'.
os: oculus sinister, meaning 'left eye'.
ou: oculus uterque, meaning 'both eyes'.
ad: auris dexter, meaning 'right ear'.
as: auris sinister, meaning 'left ear'.
au: auris utraque, meaning 'both ears'.

The Critical Risks of Misinterpretation

Despite their efficiency, prescription abbreviations can be a significant source of medication errors, with some studies attributing nearly 5% of all medication errors to their use. The ambiguity of certain abbreviations, compounded by poor handwriting, can lead to dangerous misunderstandings. For example:

U vs. Unit: The abbreviation U for "unit" has been mistaken for a '0' or a '4', leading to severe overdoses.
QD vs. QID: As mentioned, the similarity between 'QD' (once daily) and 'QID' (four times daily) is a frequent source of error, potentially leading to a fourfold increase in dose.
D/C: This can mean either 'discontinue' or 'discharge', creating potential for misinterpretation in a hospital setting.
Drug Name Abbreviations: Shortcuts for drug names, such as 'MS' for morphine sulfate, can be mistaken for 'magnesium sulfate,' with devastating consequences.

Enhancing Patient Safety Through Standardized Practices

To combat these risks, health organizations worldwide have implemented standardized practices. The most prominent example is the creation of "Do Not Use" lists, which mandate that certain high-risk abbreviations and symbols never be used in prescriptions. Hospitals and pharmacies often audit prescriptions to ensure compliance and promote patient safety. Technology also plays a vital role.

Electronic prescribing (e-prescribing) has emerged as a major solution to reduce errors associated with handwritten prescriptions. By converting a prescriber's order into a standardized, digital format, e-prescribing eliminates illegible handwriting and forces the use of full, clear terms rather than ambiguous abbreviations. This ensures the pharmacist receives a precise, easily understandable set of instructions, greatly reducing the risk of misinterpretation.

Comparison of Common Prescription Abbreviations


Abbreviation	Latin Root	Meaning	Potential Risk	Safe Alternative
b.i.d.	bis in die	twice a day	Low risk	"twice daily"
t.i.d.	ter in die	three times a day	Low risk	"three times daily"
q.i.d.	quater in die	four times a day	Low risk (though often confused with QD)	"four times daily"
q.d.	quaque die	every day	High Risk (confused with QID, QOD)	"daily" or "every day"
q.o.d.	quaque [other] die	every other day	High Risk (confused with QD, QID)	"every other day"
h.s.	hora somni	at bedtime	Moderate Risk (confused with "half strength")	"at bedtime" or "every night"
p.r.n.	pro re nata	as needed	Moderate risk (requires patient understanding)	"as needed"
p.o.	per os	by mouth	Low risk	"by mouth" or "orally"

Conclusion

While prescription abbreviations have a long history rooted in efficiency, their modern application has highlighted the significant safety risks they pose. Ambiguous abbreviations can lead to misinterpretation and potentially harmful medication errors. With the advent of technologies like e-prescribing and the widespread adoption of "Do Not Use" lists, the healthcare industry is moving toward more explicit and standardized communication. This shift not only improves safety for patients but also enhances the trust and clarity of the prescribing process. As a patient, understanding these common abbreviations and never hesitating to ask your pharmacist for clarification is a vital step in taking control of your health.

For more information on safe medication practices, see the Institute for Safe Medication Practices (ISMP) website.

Frequently Asked Questions

BID is an abbreviation for bis in die, a Latin phrase meaning 'twice a day.' When you see this on a prescription, it means you should take the medication approximately every 12 hours.

'PRN' stands for pro re nata, which means 'as needed.' This instruction is often used for medications like pain relievers or anti-anxiety drugs that are not taken on a fixed schedule.

'PO' comes from the Latin term per os, meaning 'by mouth' or 'orally.' It indicates that the medication should be taken by swallowing, rather than another route of administration.

Abbreviations like 'QD' (once daily) are on "Do Not Use" lists because they can be easily confused with other abbreviations, particularly 'QID' (four times daily). This mix-up can lead to a dangerous over-dosing error.

If you cannot read or are unsure about any abbreviation on your prescription, you should always ask your pharmacist or doctor for clarification. Never guess or assume the meaning, as this could lead to a medication error.

Yes, specific abbreviations are used for the eyes and ears, often to differentiate between the right, left, or both. For example, 'OD' means right eye, 'OS' means left eye, and 'OU' means both eyes.

Electronic prescribing reduces the risks associated with ambiguous abbreviations by requiring prescribers to use clear, standardized terms instead of potentially illegible handwritten shortcuts. This minimizes guesswork and promotes accuracy.