In medical shorthand, a “p” with a horizontal line (or bar) drawn over it stands for “after,” derived from the Latin word post. You will most often encounter it in prescription instructions, nursing notes, and clinical charts, where it serves as a quick way to indicate timing. A note reading “p̄ meals,” for instance, means “after meals.” The abbreviation belongs to a small family of single-letter-with-bar symbols that have been part of medical documentation for centuries, though their role is shrinking as healthcare moves toward electronic records and plainer language.
Where This Symbol Shows Up
The most common place you will run into p̄ is on a handwritten prescription or a medication administration record. A prescriber might write something like “2 tabs p̄ meals” to tell the pharmacist or nurse that two tablets should be taken after eating. In hospital nursing notes, the symbol has historically appeared in shorthand charting: “p̄ surgery, pt was alert” translates to “after surgery, the patient was alert.” It also turns up in clinical progress notes, especially older ones written in a telegraphic style where every saved letter helped a busy clinician document faster.
If you have ever squinted at a discharge summary, an old prescription label, or a nursing kardex, there is a fair chance p̄ was one of the mysterious markings. The good news is that the symbol has a single, stable meaning. It always means “after.” There is no secondary definition lurking in a different specialty.
The Other Bar-Over-a-Letter Abbreviations
The p̄ does not exist in isolation. Medical Latin shorthand uses the same convention with other letters, each representing a different common word. Knowing the full set makes any of them easier to remember and harder to confuse.
- ā (a-bar): “before,” from the Latin ante. A prescription note “ā meals” means before meals.
- c̄ (c-bar): “with,” from the Latin cum. Seen in instructions like “c̄ food,” meaning take with food.
- s̄ (s-bar): “without,” from the Latin sine. A chart note “s̄ fever” means without fever.
- p̄ (p-bar): “after,” from the Latin post.
Together these four abbreviations cover the most basic relational words in clinical timing and description: before, with, without, and after. A handful of other Latin abbreviations round out the system. You might see “q” for “every” (from quaque), “h” for “hour” (from hora), or “prn” for “as needed” (from pro re nata). None of these others use the bar convention, though, so the bar is a distinctive signal that you are looking at one of the four letters listed above.
Why a Bar Instead of Just Writing the Word
The bar-over-a-letter convention traces back to medieval Latin manuscript tradition, where scribes routinely used overlines to mark abbreviations. A bar told the reader that a word had been shortened and that the full Latin term should be mentally expanded. Medical education adopted Latin as its working language early on, and the scribal abbreviation system came along with it. Over centuries, these marks became part of the standard taught in pharmacy and nursing schools, embedded in formularies and reference manuals, and passed down through clinical apprenticeship.
From a practical standpoint, the bar was useful because it took almost no extra time to write. A clinician scrawling notes in the middle of a busy ward round could dash off “p̄” in barely more effort than a plain lowercase p. The bar is essentially a single horizontal pen stroke directly above the letter. In an era when nearly all medical documentation was handwritten and speed mattered, these micro-savings of time added up over a shift.
How p̄ Gets Confused With Other Symbols
The compactness that makes p̄ efficient also makes it risky. On a hurriedly written prescription, a p̄ can look very similar to an ā if the downstroke of the “p” is messy or if the bar drifts slightly. The consequences of swapping “after” and “before” in a medication instruction are not always trivial. Certain drugs are meant to be taken on an empty stomach (before meals) so they absorb properly, while others need food in the stomach (after meals) to avoid nausea or stomach irritation. Getting that timing backward can reduce a drug’s effectiveness or increase side effects.
Handwriting variability is the core problem. A bar that is too short can be missed entirely, turning “p̄” into a plain “p,” which in some prescription contexts might be read as a different abbreviation altogether. Conversely, a “q” (meaning “every”) written sloppily can resemble a “p,” and adding a stray mark on top can make it look like p̄. Research into medication errors tied to abbreviation misinterpretation has consistently found that single-letter shorthand is among the more error-prone documentation habits in clinical settings.1PubMed Central. Avoiding Potential Medication Errors Associated with Non-intuitive Medication Abbreviations
The Push to Retire Latin Abbreviations
Because of these risks, major patient-safety organizations have spent years encouraging healthcare professionals to stop using Latin abbreviations in clinical documentation. The Institute for Safe Medication Practices (ISMP) maintains a list of error-prone abbreviations that it recommends against. The Joint Commission, which accredits hospitals in the United States, publishes its own “Do Not Use” list, targeting abbreviations most likely to cause harm. While p̄ and the other bar-letter abbreviations are not always on the formal “Do Not Use” list by name, they fall squarely under the broader recommendation to write out words fully rather than rely on symbols that are easily misread.
The argument for retiring these abbreviations is straightforward: writing “after meals” takes only a moment longer than writing “p̄ meals,” and the clarity gain is enormous. A patient, a pharmacist, a nurse, or another physician reading the note will never misinterpret the word “after.” The same cannot be said for a tiny handwritten letter with an ambiguous bar.2PubMed Central. It’s time to throw out old-fashioned Latin abbreviations
Nursing and pharmacy programs have gradually shifted their curricula. Many still teach students to recognize the abbreviations (since older charts, textbooks, and some practicing clinicians still use them) but discourage students from writing them in their own documentation. The result is a generational fade: a nurse who trained in the 1980s might use p̄ reflexively, while a nurse who trained in 2020 might need a moment to recall what it means.
What Electronic Health Records Changed
The transition from handwritten charts to electronic health records (EHRs) has done more to reduce p̄ usage than any policy change. In an EHR, medication orders are typically entered through structured fields: you select the drug, the dose, the route, and the timing from dropdown menus or preset options. There is no opportunity to scrawl “p̄ meals” because the system forces you to choose “after meals” from a list. The abbreviation becomes unnecessary.
Some handwritten prescriptions still exist, particularly in outpatient clinics, certain specialty settings, and countries where EHR adoption is less universal. For those contexts, efforts to digitize handwritten prescriptions using optical character recognition and natural-language processing are underway. One recent system designed to read handwritten prescriptions achieved roughly 90 percent accuracy in extracting and standardizing drug names, dosages, and instructions, though that still leaves a meaningful error rate for safety-critical documents.3IEEE Xplore. A Deep Learning-Based Framework for Handwritten Medical Prescription Recognition Using OCR and NLP Until those technologies are good enough to reliably parse a hurried clinician’s shorthand, the safest approach remains writing in full.
Reading Your Own Medical Records
If you are looking at your own medical chart, discharge papers, or a prescription and you spot a “p” with a line over it, now you know what it means. But there are a few practical points worth keeping in mind.
First, context matters for timing instructions. “p̄ meals” on a medication label tells you to take the drug after eating, but it does not tell you how long after. In most cases, “after meals” means shortly after finishing a meal, not two hours later. If precise timing matters for your medication, ask your pharmacist rather than guessing from an abbreviation.
Second, if you see an abbreviation on your prescription that you cannot identify, do not try to decode it on your own. Pharmacists are trained to interpret medical shorthand and will confirm the prescriber’s intent. Guessing incorrectly could lead you to take a medication at the wrong time, in the wrong dose, or by the wrong route. This is exactly the scenario that patient-safety advocates worry about when they argue against abbreviation use.
Third, you have the right to understand your own medical records. Many countries, including the United States under the 21st Century Cures Act, guarantee patients access to their clinical notes. If you are reading through your chart and encounter unfamiliar symbols, your care team is obligated to explain them. The whole point of open access to records is to improve understanding between patients and providers, and decoding Latin shorthand is a reasonable part of that conversation.
Related Prescription Abbreviations You Might Encounter
Once you start reading prescriptions or clinical notes, p̄ is rarely the only unfamiliar marking. A few other abbreviations show up so frequently that they are worth knowing, even as they, too, are gradually being written out in full.
- b.i.d.: twice a day, from bis in die.
- t.i.d.: three times a day, from ter in die.
- q.i.d.: four times a day, from quater in die.
- q.d.: once a day, from quaque die. This one is on the Joint Commission’s “Do Not Use” list because “q.d.” is easily confused with “q.i.d.” in handwriting, potentially quadrupling a dose.
- p.o.: by mouth, from per os.
- p.r.n.: as needed, from pro re nata.
- Rx: the familiar prescription symbol, thought to derive from the Latin recipe, meaning “take.”
Notice that several of these are multi-letter abbreviations with periods between the letters, unlike the bar-over-a-letter system. The periods serve a similar function to the bar: they signal that the letters are an abbreviation rather than a word. But they bring their own misreading risks. A period after “q” can be mistaken for a “1” in hasty handwriting, turning “q.d.” (once daily) into “q1d” or, worse, into something unintended. These kinds of look-alike errors are the reason safety organizations want clinicians to simply write “once daily,” “twice daily,” or “after meals” in plain language.
When You Might Still Need to Know These Symbols
Even though the trend is firmly toward writing things out, Latin medical abbreviations have not vanished. They persist in several contexts where you might encounter them without warning. Old paper records are one obvious example. If you request historical medical records from a hospital or clinic that predates full EHR adoption, you may receive pages of handwritten notes peppered with symbols like p̄, ā, and c̄. Pharmacy compounding logs, especially in independent pharmacies with long-running practices, sometimes still use traditional shorthand. And internationally, the pace of change varies. Clinicians in some countries continue to train with Latin abbreviations as the default, particularly where English is not the working language of healthcare and where local formularies have not adopted the safety recommendations common in North American and European systems.
Veterinary medicine is another holdout. Prescriptions for animals often use the same Latin abbreviation system, and pet owners who receive written instructions from a vet may find themselves staring at “p̄ feeding” or “c̄ food” without a pharmacist standing by to translate. If you are managing a pet’s medication regimen and see these symbols, the same rules apply: p̄ means after, ā means before, c̄ means with, s̄ means without. When in doubt, call the clinic.
Academic textbooks and licensing exams represent yet another place where these abbreviations linger. Nursing board exams, pharmacy licensing tests, and medical school assessments still test knowledge of Latin abbreviations, partly because clinicians need to read older documentation and partly because the abbreviations remain in use just often enough to be clinically relevant. Students sometimes complain that they are being asked to memorize symbols their instructors simultaneously tell them never to write. The tension is real, but it reflects where healthcare documentation actually stands: in transition, not yet fully transitioned.