PO BID on a prescription means “by mouth, twice a day.” Your doctor is telling you to take the medication orally (swallowing it) two times per day. These are Latin-based abbreviations still widely used in medical prescriptions: PO comes from “per os” (by mouth) and BID from “bis in die” (twice in a day).
What PO Means
PO tells you the route of administration, which is simply how the medication enters your body. In this case, you swallow it. That could be a tablet, capsule, liquid solution, syrup, or any other form designed to be taken by mouth. PO distinguishes oral medications from those applied to the skin, injected, inhaled, or administered in other ways.
You might occasionally see the full Latin phrase “per os” written out instead. The Institute for Safe Medication Practices actually recommends using the abbreviation “PO” over spelling out “per os,” because “os” can be misread as “OS,” which is the abbreviation for “left eye.” That mix-up has led to real medication errors.
What BID Means
BID means you take the medication twice daily. In hospital settings, standard BID dosing is typically scheduled at 9:00 a.m. and 9:00 p.m., spacing doses roughly 12 hours apart. At home, your pharmacist will usually translate this to something like “take one tablet by mouth twice daily” on the prescription label, and morning and evening is the most common interpretation.
The 12-hour spacing matters more for some medications than others. Antibiotics, pain medications, and anti-seizure drugs generally need to be taken at evenly spaced intervals to maintain a steady level in your bloodstream. For other medications, the exact timing is less critical, and “twice a day” with breakfast and dinner works fine. Your pharmacist’s label or your doctor’s specific instructions will clarify if precise timing matters for your particular drug.
How BID Compares to Similar Abbreviations
Prescriptions use a whole family of frequency abbreviations. Knowing where BID fits helps you read any prescription label:
- QD: once a day
- BID: twice a day
- TID: three times a day
- QID: four times a day
- Q12H: every 12 hours (similar to BID but stricter on timing)
BID and Q12H look interchangeable, but there’s a subtle difference. Q12H means exactly every 12 hours, with no flexibility. BID gives a bit more leeway. If your prescription says Q12H, stick to a precise 12-hour schedule. If it says BID, morning and evening dosing with roughly equal spacing is generally fine.
What to Do If You Miss a Dose
For most twice-daily medications, take the missed dose as soon as you remember, as long as your next scheduled dose isn’t due within a few hours. Then go back to your regular schedule. Don’t double up by taking two doses at once.
Some higher-risk medications have tighter rules. Anti-seizure drugs taken twice daily, for example, follow a stricter guideline: take the forgotten dose if it’s within six hours of when it was due, but skip it entirely if more than six hours have passed. The specific window depends on the drug, so checking the information sheet that came with your prescription is worth the 30 seconds it takes.
Other Abbreviations You Might See With PO BID
Your prescription may include additional shorthand that modifies when or how you take your doses relative to meals:
- AC: before meals
- PC: after meals
- CC: with food
So “PO BID AC” would mean “by mouth, twice a day, before meals,” and “PO BID PC” means “by mouth, twice a day, after meals.” These meal-related instructions affect how well the drug is absorbed or whether it irritates your stomach.
If your prescription label from the pharmacy doesn’t spell things out in plain English, or if the abbreviations don’t match what your doctor told you verbally, ask your pharmacist to clarify. They translate these abbreviations every day and can confirm exactly what your prescriber intended.