What is OD and BD in medical? Understanding Your Prescription

September 22, 2025 •

4 min read

According to the Institute for Safe Medication Practices, confusion over medical abbreviations is a leading cause of medication errors. Understanding what is OD and BD in medical terms is crucial for patient safety, as these common symbols dictate how often you should take your medication.

Quick Summary

OD and BD are common medical abbreviations used on prescriptions to specify medication frequency: OD means 'once daily' and BD means 'twice daily.' These terms, derived from Latin, are crucial for ensuring correct dosage and preventing medication errors, and are often part of a larger set of prescription codes for timing and administration.

Key Points

OD: Once Daily: The abbreviation OD is a medical shorthand for 'once daily,' meaning a medication is to be taken every 24 hours.
BD: Twice Daily: BD, or sometimes BID, means 'twice daily,' with doses typically spaced 12 hours apart to maintain consistent drug levels in the bloodstream.
Context is Crucial: While OD most often means 'once daily' on a prescription, in eye care, it stands for 'right eye' (oculus dexter), so context is essential to prevent dosage errors.
Consistent Timing Matters: Whether taking a medication once or twice daily, maintaining a consistent schedule helps ensure the drug remains effective throughout the treatment period.
When in Doubt, Ask: If you are unsure about any abbreviation on your prescription, always clarify with your doctor or pharmacist to avoid potentially harmful medication mistakes.

Deciphering Common Prescription Abbreviations

Prescription abbreviations can often seem like a foreign language, but they serve as a critical communication tool between a prescriber and a pharmacist to ensure a patient receives the correct medication and instructions. When you see letters like OD and BD, it's about the timing and frequency of your dose. Proper understanding is the first step toward effective treatment and a safer healthcare experience.

What Does OD Stand For?

OD, or 'omnie in die' in Latin, simply means 'once daily'. A prescription with 'OD' indicates that the medication should be taken one time every 24 hours. The timing may depend on the specific medication—some might be best taken in the morning, others at night—but the key is consistency. Taking the medication around the same time each day helps maintain a steady level of the drug in your body, which can be essential for its effectiveness.

It is important to note a potential source of confusion: in optometry, OD stands for 'oculus dexter,' meaning 'right eye'. However, in the context of a drug prescription for oral medication, it refers to the daily frequency. If you receive a prescription with OD for an eye-related issue, it is vital to confirm with your pharmacist whether it means 'once daily' or 'right eye' to avoid any dangerous misunderstandings.

What Does BD Stand For?

BD, derived from the Latin 'bis in die,' translates to 'twice daily'. This instructs patients to take their medication two times a day, typically with a 12-hour interval, such as morning and night. For many drugs, maintaining a more consistent level in the bloodstream is crucial, and a twice-daily regimen helps achieve this balance.

While BD is the common shorthand, you might also see BID, which is the more formal Latin abbreviation but means the exact same thing. Like with OD, consistent timing is important, and for certain medications, taking them with or without food might also be a factor that influences the schedule.

Comparing OD vs. BD: Key Differences and Implications

Understanding the difference between OD and BD is fundamental for patient compliance and therapeutic efficacy. Here is a quick comparison:


Aspect	OD (Once Daily)	BD (Twice Daily)
Meaning	Once a day	Twice a day
Timing	Every 24 hours	Every 12 hours
Latin Origin	Omnie in die	Bis in die
Use Case	Medications with a long half-life that can maintain a therapeutic level with one dose.	Medications that require more consistent blood levels throughout the day for optimal effect.
Patient Adherence	Simpler for patients to remember, reducing the risk of a missed dose.	Requires more frequent reminders and consistent scheduling throughout the day.

The Importance of Correct Dosage

Misinterpreting OD and BD can have serious consequences. Taking a once-daily medication twice a day can lead to an overdose, causing dangerous side effects or toxicity. Conversely, taking a twice-daily medication only once a day might result in the drug's concentration dropping too low in the body to be effective.

Context is Key: More Prescription Abbreviations

Beyond OD and BD, many other abbreviations can be found on prescriptions. Some of the most common include:

TID (ter in die): Three times a day
QID (quater in die): Four times a day
QD (quaque die): Once daily (some institutions discourage use due to confusion with QID)
PRN (pro re nata): As needed
STAT (statim): Immediately
HS (hora somni): At bedtime
AC (ante cibum): Before meals
PC (post cibum): After meals

These abbreviations add context and detail to a prescription, creating a comprehensive set of instructions for the patient. A clear understanding of these terms helps build patient confidence and improves health outcomes.

Your Role in Ensuring Medication Safety

While healthcare professionals are trained to write and interpret these abbreviations correctly, patients also have a role to play. Whenever you receive a new prescription, it's wise to review it and ask questions. Don't hesitate to ask your pharmacist or doctor to clarify the instructions in plain language. If you ever have a doubt about what a symbol means, asking for clarification is the safest course of action.

In some regions, healthcare authorities are encouraging the use of clearer, spelled-out instructions to minimize the risk of error. For example, instead of OD or QD, the prescription might explicitly say 'once daily'. This practice aims to reduce the possibility of misinterpretation and enhance patient safety.

Understanding the language of your prescription, including key terms like OD and BD, is a powerful tool for taking control of your health. Knowledge empowers you to be an active and informed participant in your own care, ensuring you use your medications safely and effectively.

For more information on safe medication practices, consult authoritative resources like the Institute for Safe Medication Practices (ISMP).

Frequently Asked Questions

These abbreviations are derived from Latin terms. OD comes from omnie in die (once daily), and BD comes from bis in die (twice daily).

No, several other common abbreviations exist, including TID (three times a day), QID (four times a day), and PRN (as needed).

Knowing these abbreviations is essential for patient safety. Misinterpreting them could lead to an incorrect dosage, which can be ineffective or even dangerous.

In ophthalmology, OD can mean 'right eye,' while BD can sometimes be confused with other terms. Always clarify with your pharmacist to ensure you use the drops as intended, preventing potential harm.

BD and BID mean the same thing: twice daily. BID is a more formal Latin abbreviation, bis in die, but both refer to taking medication two times per day.

Yes, consistency is key. Taking the medication at the same time each day helps maintain a stable level of the drug in your system. Your doctor or pharmacist can advise on the best time for your specific medication.

For many medications, yes. Taking the doses approximately 12 hours apart, such as morning and night, helps ensure the drug concentration remains at a therapeutic level in your body throughout the day.