Medical Prescription Abbreviations: A Comprehensive Guide

Medical prescriptions often contain abbreviated Latin terms that can be confusing to patients and even healthcare providers who are not familiar with them. These abbreviations have been used for centuries and are still employed in medical writing today. Understanding these prescriptions is crucial for safe medication use. This guide explores the most common prescription abbreviations, their meanings, and why knowledge of them is important for patient safety.

Frequency Abbreviations

One of the most important aspects of a prescription is how often a medication should be taken. Here are common abbreviations related to dosage frequency:

Abbreviation	Meaning
q.d. or QD	Once daily (every day)
b.i.d. or BID	Twice daily
t.i.d. or TID	Three times daily
q.i.d. or QID	Four times daily
q.h. or qH	Every hour
q.2h., q.3h., etc.	Every 2 hours, every 3 hours, etc.
q.a.m.	Every morning
q.p.m.	Every evening
q.o.d.	Every other day
q.w.	Every week

Dosage-Related Abbreviations

These abbreviations relate to the quantity or amount of medication to be taken:

Abbreviation	Meaning
g or gm	Gram
mg	Milligram
g or mcg	Microgram
ng	Nanogram
L	Liter
mL	Milliliter
gtt	Drop
tab	Tablet
cap	Capsule
ss	One-half (semisse)
u or um	Unit

Route of Administration Abbreviations

These abbreviations indicate how the medication should be administered:

Abbreviation	Meaning
p.o. or PO	Orally/By mouth (per os)
s.l. or SL	Sublingually (under the tongue)
i.v. or IV	Intravenously/Into a vein
i.m. or IM	Intramuscularly/Into a muscle
s.c. or SC	Subcutaneously/Below the skin
i.n.	Intranasally/Into the nose
p.r.	Rectally
p.v. or PV	Vaginally
top	Topically/On the skin
od	Right eye
os	Left eye
ou	Both eyes

Timing and Meal-Related Abbreviations

These abbreviations specify when to take medication in relation to meals:

Abbreviation	Meaning
a.c.	Before meals (ante cibum)
p.c.	After meals (post cibum)
aa.	Of each (ana)
ad lib.	As needed or freely (ad libitum)
prn	As needed (pro re nata)
stat	Immediately (statim)
c. or	With (cum)
s. or s	Without (sine)
n.p.o.	Nothing by mouth (nil per os)

Other Common Prescription Abbreviations

Miscellaneous abbreviations frequently found in prescriptions:

Abbreviation	Meaning
D/C	Discontinue
D.S.	Double strength
E.D.D.	Expected date of delivery
et	And
f.t.	Following
h.s.	At bedtime (hora somni)
i.c.	Between meals (inter cibus)
inj.	Injection
N / N	Noon
Noct	Night
o.d. or OD	Once daily (in context of frequency)
p.m.	Afternoon or evening (post meridiem)
p.r.n. or PRN	As needed
Rx	Prescription or remedy
s.o.s.	If needed (si opus sit)
sup	Suppository
tid	Three times a day (ter in die)

Safety Considerations with Prescription Abbreviations

The use of abbreviations in prescriptions has been a long-standing tradition in medicine, but concerns about patient safety have led many healthcare organizations to discourage or outright ban certain abbreviations deemed particularly dangerous. The Institute for Safe Medication Practices (ISMP) maintains a list of "dangerous abbreviations" that should be avoided to prevent medication errors.

Common Problematic Abbreviations

• Q.D. (once daily) vs Q.O.D. (every other day) - The dot after Q can be mistaken as an "I", confusing the frequency
• U (unit) - Can be mistaken for 0, 4, or cc
• g (microgram) - The can be mistaken for m, resulting in milligrams being administered instead of micrograms
• IU (international unit) - Can be mistaken for IV (intravenous) or 10
• MS (morphine sulfate or magnesium sulfate) - Ambiguous abbreviation

The Trend Toward Plain Language

In recent years, there has been a movement away from Latin abbreviations in favor of plain language instructions. Many healthcare systems now require written prescriptions to use clear, unambiguous language such as "once daily" instead of "QD" or "take every morning" instead of "q.a.m."

This shift recognizes that patients increasingly need to understand their own medication instructions, and that clear communication is essential for medication adherence and safety. Electronic prescribing systems have also contributed to this change by often requiring complete words rather than abbreviations.

Understanding Your Prescription

Despite these changes, medical students are still taught Latin abbreviations, and they remain widely used in clinical settings. As a patient, understanding these abbreviations can help you:

• Take your medications correctly
• Recognize potential errors in your prescription
• Communicate more effectively with your healthcare providers
• Better manage your medication schedule

Tips for Safe Medication Use

1. Always ask your healthcare provider or pharmacist to explain any abbreviation you don't understand
2. Keep a current list of all your medications, including dosages and timing
3. Read the patient information leaflet that comes with your medication
4. Ask about potential interactions with other medications, food, or supplements
5. Report any side effects to your healthcare provider

Conclusion

Medical prescription abbreviations have their roots in ancient Latin and continue to be used in modern healthcare. While the healthcare industry is moving toward clearer, plain language instructions, understanding these traditional abbreviations remains valuable for anyone who wants to comprehend their prescriptions fully.

Patient safety should always be the priority. If you have any uncertainty about how to take your medicationthe timing, the amount, or the methoddon't hesitate to ask your doctor, nurse, or pharmacist for clarification. Clear understanding is the key to safe and effective medication use.