“PO BID” is a prescription shorthand meaning “by mouth, twice a day.” You’ll typically see it on medication labels, pharmacy printouts, or doctor’s notes. The two parts come from Latin: PO stands for “per os” (by mouth), and BID comes from “bis in die” (twice in a day).
Breaking Down Each Part
PO tells you the route: swallow the medication by mouth. This is the most common way medications are given because it’s convenient and cost-effective. PO specifically means swallowing the drug so it travels through your digestive system. It does not include placing a tablet under your tongue (sublingual) or tucking it against your cheek (buccal), which are separate routes designed to get medication into your bloodstream faster by bypassing the liver.
BID tells you the frequency: take it twice a day. Together, PO BID on a prescription means you should swallow one dose by mouth, two times per day.
BID vs. Every 12 Hours
“Twice daily” and “every 12 hours” are not always the same thing. As MD Anderson Cancer Center notes, “take twice daily” leaves room for interpretation, while “every 12 hours” requires more precision. Some medications need to stay at a steady level in your bloodstream, so the timing between doses matters. Others are more flexible.
If your prescription says “every 12 hours,” aim for doses spaced as close to 12 hours apart as possible. That could be 8 a.m. and 8 p.m., or 7 a.m. and 7 p.m. If it simply says “twice daily” without specifying hours, ask your pharmacist whether even spacing is important for that particular drug.
Other Frequency Abbreviations
BID fits into a family of Latin-based shorthand you may see on prescriptions:
- QD (quaque die): once a day
- BID (bis in die): twice a day
- TID (ter in die): three times a day
- QID (quater in die): four times a day
- PRN (pro re nata): as needed
- QOD: every other day
You may also see timing instructions like “AC” (before meals) or “PC” (after meals), which tell you whether to take the medication on an empty or full stomach.
Why Abbreviations Sometimes Cause Confusion
These shorthand terms save space, but they can be misread. The Institute for Safe Medication Practices maintains a list of error-prone abbreviations. One common mix-up: “BT” (intended to mean bedtime) has been mistaken for “BID,” leading a patient to take a medication twice daily instead of once at night. Similarly, writing out “per os” longhand can be misread as “OS,” which in ophthalmology means “left eye.” That’s why pharmacies generally use “PO” or spell out “by mouth” instead.
Modern electronic prescribing systems have reduced these errors, but if anything on your prescription label looks unclear, your pharmacist can confirm exactly what was intended.
What to Do if You Miss a BID Dose
General guidance for twice-daily medications: if you remember within about two hours of when you should have taken it, go ahead and take the missed dose. If it’s been longer than that, take the missed dose as long as your next scheduled dose isn’t coming up within a few hours. Then resume your normal schedule.
Never double up to make up for a forgotten dose unless a prescriber has specifically told you to. Taking two doses close together increases the risk of side effects without providing extra benefit for most medications. If you’re consistently forgetting doses, setting phone alarms for your two daily times can help you stay on track.