Meaning of OD, BD, TDS and SOS in a Doctor’s Prescription
Learn the meaning of OD, BD, TDS, and SOS in medical prescriptions. Understand their importance in medication schedules for safe and effective treatment.

Medical prescriptions often include abbreviations like OD, BD, TDS, and SOS, which can confuse patients. These shorthand terms streamline communication among healthcare professionals, ensuring clear and concise treatment instructions. Understanding these abbreviations is vital for following medication schedules accurately, preventing errors, and achieving the best treatment outcomes. This article explains the meanings of common prescription abbreviations, including “once daily” or “omni die” (OD), “bis in die” (BD), “ter die sumendum” (TDS), and “si opus sit” (SOS), and highlights their importance in medical treatment.
OD: “Once Daily”
The abbreviation “OD” is short for “once daily” or “omni die” in Latin. When a doctor writes “OD” on a prescription, it means the medication should be taken once every day. This is often seen in treatments that require consistent, daily dosages to maintain effectiveness, such as antibiotics or medications for chronic conditions like hypertension or diabetes.
For example, if a doctor prescribes a blood pressure medication with the instruction “OD,” the patient should take one dose at a specific time each day, as regularity ensures stable blood levels of the drug.
BD: “Twice Daily”
“BD,” which stands for “bis in die” (Latin for “twice daily”), indicates that the medication should be taken twice per day. This is typically used for medications that have a shorter duration of action, meaning the drug needs to be administered more frequently to maintain its effectiveness throughout the day.
A common scenario might involve painkillers or certain antibiotics that require a morning and evening dose to control symptoms or infections effectively. Following this prescription properly ensures the medication works as intended without peaks and troughs in drug levels.
TDS: “Three Times Daily”
“TDS” stands for “ter die sumendum” or “three times daily.” This instruction is used for medications that require more frequent dosing, often to ensure that the active ingredient stays within therapeutic levels in the body. Some medications metabolize quickly, and taking them only once or twice a day would result in ineffective treatment or gaps where symptoms might return.
For example, certain antibiotics or antacids might require dosing three times a day to continuously fight an infection or control stomach acid production.
SOS: “As Needed”
“SOS” originates from the Latin “si opus sit,” meaning “if necessary” or “as needed.” When “SOS” is included on a prescription, the medication is only to be taken when the patient feels the need for it, typically for symptom relief. This is commonly seen in pain medications, anti-nausea drugs, or treatments for acute conditions where the patient’s symptoms may not be constant.
A prescription for migraine relief might include “SOS,” indicating that the patient should only take the medication when a migraine occurs, rather than on a fixed schedule.
The Importance of Following Prescription Abbreviations
Understanding prescription abbreviations such as OD, BD, TDS, and SOS is crucial for following medical advice correctly. Misinterpreting these terms can lead to under- or over-dosing, which may either reduce the effectiveness of the treatment or cause adverse effects. For example, taking a medication labeled “BD” once a day instead of twice might not provide the necessary therapeutic benefit, while taking it more than twice could lead to overdose.
Additionally, knowing when to take a medication “bis in die” (twice daily) versus “si opus sit” (as needed) helps patients manage their conditions effectively, whether it’s for chronic disease control or acute symptom relief.
Conclusion
Understanding common prescription abbreviations like OD, BD, TDS, and SOS is essential for correctly taking your medication. OD means “once daily,” BD means “twice daily,” TDS means “three times daily,” and SOS means “as needed.” Following these instructions accurately ensures the best and safest treatment outcomes. Patients should always consult their healthcare provider or pharmacist if they are unsure about their prescription to avoid errors and enhance their care.
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- Posted by Dayyal Dg.