B.i.d. is a medical abbreviation from the Latin phrase “bis in die,” meaning twice a day. You’ll see it on prescriptions, medication labels, and medical charts to indicate that a medication should be taken two times daily, typically spaced about 12 hours apart.
What B.I.D. Means on a Prescription
When a prescription reads “b.i.d.,” it’s telling you (or the pharmacist) that the medication should be taken twice daily. The ideal spacing is every 12 hours, which keeps the drug at a steady level in your bloodstream throughout the day. In practice, most people take their b.i.d. medication once in the morning and once in the evening, often around breakfast and dinner.
The exact timing matters more for some drugs than others. Antibiotics and blood pressure medications generally need that consistent 12-hour gap to work properly. Other twice-daily medications are more forgiving if your schedule shifts by an hour or two. Your pharmacist can tell you how strict the timing needs to be for your specific prescription.
How B.I.D. Compares to Other Dosing Terms
B.i.d. is one of several Latin abbreviations still used in prescribing. Here’s how the most common ones break down:
- Q.D. (quaque die): once a day
- B.I.D. (bis in die): twice a day, roughly every 12 hours
- T.I.D. (ter in die): three times a day, roughly every 8 hours
- Q.I.D. (quater in die): four times a day
The fewer times a day you need to take a medication, the easier it is to stay on track. A large study of over one million patients with cardiovascular conditions found that people prescribed once-daily versions of their medications were consistently more adherent than those on twice-daily regimens. For one common heart medication, carvedilol, patients taking the once-daily formulation filled their prescriptions 11% more reliably than those on the b.i.d. version. This is one reason pharmaceutical companies often develop extended-release versions of drugs: reducing the number of daily doses makes it more likely people will actually take them.
Why These Abbreviations Are Fading
Although b.i.d. is still widely recognized, the healthcare industry has been moving away from Latin prescription abbreviations for safety reasons. The Joint Commission, which accredits hospitals in the United States, maintains a “Do Not Use” list of abbreviations that can lead to medication errors. The concern is that similar-looking abbreviations, especially in handwritten notes, can be confused with one another. “Q.D.” (once daily) and “Q.I.D.” (four times daily) are particularly easy to mix up.
Electronic health records have eliminated the legibility problem, but they haven’t solved the abbreviation issue entirely. One hospital study found that medication abbreviations were the most common type of prohibited abbreviation appearing in electronic records, accounting for 78% of all flagged entries. After staff education, usage dropped significantly, but old habits proved hard to break. Many modern prescribing systems now default to plain English, printing “take twice daily” instead of “b.i.d.” on prescription labels you receive at the pharmacy.
What to Do If You Miss a B.I.D. Dose
If you’re less than two hours late, take the dose as soon as you remember. For most twice-daily medications, a small delay won’t meaningfully affect how the drug works in your body.
If you’re more than two hours late, take the missed dose as long as your next scheduled dose isn’t coming up within a few hours. If it is, skip the missed dose and resume your normal schedule. The key rule: never double up to compensate for a missed dose unless your prescriber has specifically told you to. Taking two doses close together can spike drug levels in your blood and increase the risk of side effects.
Common Medications Prescribed B.I.D.
Twice-daily dosing is common across many drug categories. Some of the most frequently prescribed b.i.d. medications include certain blood pressure drugs, blood sugar medications for type 2 diabetes, cholesterol-lowering agents, and antiplatelet drugs used to prevent blood clots. Many antibiotics also follow a b.i.d. schedule, as do some antidepressants and anti-inflammatory drugs.
Whether a medication is prescribed once, twice, or more times daily depends on how long the drug stays active in your body. Medications that are metabolized quickly need more frequent dosing to maintain effective levels. If you find a b.i.d. schedule difficult to maintain, it’s worth asking your doctor whether a once-daily alternative exists for your medication. In many cases, one does.