What BD, TDS, OD, HS and SOS mean on an Indian prescription

BD means twice a day. TDS means three times a day. OD means once a day. HS means at bedtime. SOS means only if it's needed. Those five cover most of what you'll see on a prescription written for a parent in India — the rest of this guide covers the ones that come up less often but still trip people up.

Why Indian prescriptions use Latin shorthand at all

The abbreviations aren't random. They're shortened Latin, and doctors everywhere were trained on the same convention — it just survives more visibly on a handwritten Indian prescription than on a printed American one. BD is bis in die ("twice a day"). TDS is ter die sumendum ("to be taken three times a day"). OD is omni die ("every day"). HS is hora somni ("at the hour of sleep"). SOS is si opus sit ("if the occasion arises"). Knowing the origin doesn't change what to do with them, but it does explain why the same handful of letters shows up on every prescription regardless of which doctor wrote it.

The full reference

Frequency

• OD — once a day
• BD (also written BID) — twice a day
• TDS (also TID) — three times a day
• QID — four times a day
• HS — at bedtime, once
• SOS — only when needed, not on a fixed schedule
• STAT — immediately, a one-time dose, usually for something urgent

Timing relative to food

• AC — before food (ante cibum)
• PC — after food (post cibum)
• HS can also appear combined with food timing, e.g. "PC HS" — after dinner, at bedtime

Route

• PO — by mouth
• SL — under the tongue
• IM — injected into muscle
• IV — injected into a vein
• PR — rectally (uncommon, but it does appear)

On the prescription itself

• Rx — the instruction to dispense (from the Latin recipe, "take")
• Tab. / Cap. / Syr. — tablet, capsule, syrup
• Ds — dispense this quantity
• Sig — the instructions to the patient (short for signa, "label")

Reading a real line

A typical line looks like:

Tab. Metformin 500mg BD x 30 days

That's: one 500mg tablet of Metformin, taken twice a day, for a 30-day course. If it instead read "Tab. Metformin 500mg BD AC x 30 days," the AC adds that both doses should come before meals — a detail that matters for how the medicine works and is easy to miss on a fast read.

What to do when it's still ambiguous

Two things make Indian prescriptions genuinely hard to read from a photo on a phone: handwriting, and abbreviations that overlap (a hurried "TDS" and "TID" can look identical, and both mean the same thing anyway — so that one usually doesn't matter). What does matter is when a dose, a drug name, or a duration is illegible. Don't guess. Call the clinic or the pharmacy that's meant to fill it — they can read their own doctor's hand far more reliably than shorthand rules can substitute for it.

It also helps to keep the current medication list separate from the historical one. A parent seeing three doctors ends up with prescriptions that overlap, get renewed, or quietly get discontinued without anyone updating a master list — which is its own kind of risk, distinct from misreading an abbreviation. What to ask at a follow-up appointment covers the questions that keep that list honest.

Apta reads dosage shorthand like the abbreviations above straight off a photographed prescription and adds it to a parent's medication list automatically — so the decoding above becomes a one-time read, not something you redo for every new prescription that lands in the family WhatsApp chat.

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This is a reference for reading dosage instructions, not medical advice. If any part of a prescription is unclear, confirm it with the prescribing doctor or dispensing pharmacist before it affects a dose.