You are looking at a prescription or hospital medication order and it says “PO” after the drug name and dose. If you have never worked in healthcare, that abbreviation might not mean anything to you. What does PO mean in medical terms? PO stands for “per os,” a Latin phrase meaning “by mouth.” It is the most common route of administration abbreviation in medicine, indicating that a medication should be swallowed orally — as a tablet, capsule, liquid, or dissolvable form. The vast majority of medications you take at home are PO drugs, even if the prescription does not always spell it out. Understanding PO and other route abbreviations helps you take your medications correctly and communicate more effectively with your healthcare providers. For more wellness information, visit our wellness guide.
PO: The Full Definition
“Per os” literally translates to “through the mouth” in Latin. When a medical order reads “Amoxicillin 500 mg PO TID,” it means take 500 milligrams of amoxicillin by mouth three times daily. The PO designation may seem redundant for pills and capsules — of course you swallow them — but in a clinical setting where medications can be administered intravenously, intramuscularly, rectally, topically, or through other routes, specifying PO eliminates ambiguity.
You will see PO written as PO, p.o., or po on prescriptions and medical records. In hospital settings, the route of administration is a required element of every medication order. According to ISMP guidelines, omitting the route of administration is a common source of medication errors — a nurse who sees “morphine 10 mg Q4H” without a route specification might administer it IV (intravenous) when the prescriber intended PO, a difference that dramatically affects the drug’s potency and onset.
PO medications include tablets, capsules, caplets, chewable tablets, orally disintegrating tablets (ODTs), liquid solutions, suspensions, and syrups. All share the same route — they enter the body through the mouth and are absorbed through the gastrointestinal tract — but the specific dosage form can affect absorption speed, convenience, and patient tolerance.
Why Route of Administration Matters
The same medication given by different routes can have vastly different effects. A 10 mg dose of morphine taken PO produces a different response than 10 mg given IV. When morphine is taken by mouth, it passes through the liver first (a process called first-pass metabolism), which breaks down a significant portion of the drug before it reaches the bloodstream. An IV dose bypasses the liver entirely, delivering the full dose directly to the circulation. This is why oral opioid doses are typically much higher than IV doses for the same pain relief.
Route of administration affects three key pharmacological factors: bioavailability (what percentage of the drug reaches the bloodstream), onset of action (how quickly the drug starts working), and duration of effect (how long the drug remains active). PO medications generally have moderate bioavailability (varying widely by drug), a slower onset (30 to 90 minutes for most), and a longer duration compared to IV administration.
For most outpatient prescriptions, PO is the default route because it is convenient, painless, and does not require medical equipment. Patients can self-administer PO medications at home without assistance. When a patient cannot take medications by mouth — due to nausea, vomiting, unconsciousness, swallowing difficulties, or the need for rapid drug delivery — alternative routes become necessary.
PO vs Other Routes of Administration
Medical orders use a set of standard abbreviations for different routes. Understanding how PO compares to these alternatives helps you interpret medical documents and understand why your doctor chooses a particular route.
IV (intravenous): Medication delivered directly into a vein. Fastest onset (seconds to minutes), 100% bioavailability, used in hospitals for emergencies and when PO is not possible. IM (intramuscular): Injected into a muscle, such as the deltoid or thigh. Moderate onset (15 to 30 minutes), used for vaccines, certain antibiotics, and medications that are poorly absorbed PO. SubQ or SC (subcutaneous): Injected under the skin. Used for insulin, blood thinners (heparin), and some biologics. PR (per rectum): Administered rectally, typically as a suppository. Used when oral administration is not possible due to nausea or unconsciousness. SL (sublingual): Dissolved under the tongue. Nitroglycerin for chest pain is a classic SL medication — it absorbs rapidly through the oral mucosa, bypassing first-pass metabolism. TOP (topical): Applied to the skin surface. Includes creams, ointments, patches, and gels.
When you see these abbreviations on a hospital medication administration record (MAR) or in your medical chart, they tell you (and the nursing staff) exactly how each medication should be given. Mixing up routes — giving a rectal medication orally, or injecting an oral solution — can cause serious harm.
How PO Medications Are Absorbed
When you swallow a PO medication, it travels through a specific pathway before reaching your bloodstream and target tissues. Understanding this process explains why your doctor gives instructions like “take on an empty stomach” or “take with food.”
After swallowing, the medication enters the stomach, where acidic conditions begin breaking down the dosage form (tablet coating, capsule shell). Most drug absorption occurs in the small intestine, where the large surface area and rich blood supply facilitate efficient transfer of the drug into the bloodstream. From the intestine, blood carrying the absorbed drug flows to the liver via the portal vein. The liver metabolizes a portion of the drug (first-pass metabolism) before the remainder enters the general circulation and reaches its target.
Food can affect this process significantly. Some drugs absorb better on an empty stomach because food slows gastric emptying and can bind to the drug, reducing absorption. Others absorb better with food — fatty foods, in particular, can increase the absorption of fat-soluble drugs. Certain foods interact with specific drugs: grapefruit inhibits enzymes that metabolize some statins, leading to dangerously high drug levels, and dairy products bind to tetracycline antibiotics, reducing their absorption. Always follow the AC (before meals) or PC (after meals) instructions that accompany your PO prescription.
When PO Is Not an Option
Several clinical situations make oral medication administration impossible or inadvisable. Patients who are NPO (nil per os — nothing by mouth) before surgery cannot take PO medications. Patients experiencing severe nausea and vomiting cannot keep oral medications down. People with dysphagia (difficulty swallowing) due to stroke, neurological conditions, or esophageal disorders may be unable to safely swallow tablets or capsules. Unconscious or critically ill patients in intensive care units often cannot take PO medications.
In these situations, physicians switch to alternative routes — IV for critical medications, IM or SubQ for drugs available in injectable form, PR for anti-nausea medications like promethazine, or SL/buccal for drugs that absorb through the oral mucosa. Some PO medications are available in liquid form that can be administered through a nasogastric (NG) tube or gastrostomy tube (G-tube) for patients who cannot swallow but have a functioning GI tract.
Transitioning from IV to PO (called “IV-to-oral stepdown”) is a common hospital practice. Once a patient is stable enough to eat and swallow, doctors switch medications from IV to PO to reduce infection risk from IV lines, lower costs, and facilitate discharge. According to the NIH, timely IV-to-PO transitions are associated with shorter hospital stays and fewer catheter-related infections.
Reading Your Prescription Label
Most retail pharmacy labels translate medical abbreviations into plain English, but understanding the underlying abbreviations helps you verify accuracy. A typical PO prescription might be written by your doctor as: “Lisinopril 10 mg PO QD” — take 10 milligrams by mouth once daily. Your pharmacy label would read: “Take one 10 mg tablet by mouth once daily.”
When you see PO alongside timing abbreviations like BID (twice daily), TID (three times daily), QID (four times daily), or HS (at bedtime), you can decode the full instruction. “Metformin 500 mg PO BID AC” means take 500 mg by mouth twice daily before meals. “Simvastatin 20 mg PO QHS” means take 20 mg by mouth every night at bedtime.
If your pharmacy label does not match what your doctor told you — or if any part of the directions seems confusing — call the pharmacy before taking the medication. Pharmacists verify every prescription against the prescriber’s intent and can catch transcription errors that occasionally occur during the filling process.
Frequently Asked Questions
Does PO mean I have to swallow a pill?
PO means the medication is taken by mouth, but that does not necessarily mean swallowing a whole pill. PO medications include chewable tablets, dissolvable tablets, liquid solutions, and suspensions — all of which enter the body through the mouth. If you have difficulty swallowing pills, ask your pharmacist whether your medication is available in an alternative oral form.
Can I crush a PO tablet if I cannot swallow it?
Not always. Extended-release and enteric-coated tablets should never be crushed, as this can release the entire dose at once (potentially dangerous) or expose the drug to stomach acid that destroys it. Ask your pharmacist before crushing any tablet. Many medications are available in liquid or dissolvable forms that eliminate the need to crush.
What does NPO mean?
NPO stands for “nil per os” — nothing by mouth. It means you should not eat, drink, or take any oral medications. NPO orders are common before surgery, certain medical procedures, and for patients with specific GI conditions. If you are NPO and need to take essential medications, your doctor will arrange an alternative route (typically IV).
Why do some medications say “take on an empty stomach”?
Some drugs absorb better without food in the stomach. Food can delay gastric emptying, bind to the drug, or alter stomach pH in ways that reduce absorption. Thyroid medication (levothyroxine) and certain antibiotics (tetracycline) are classic examples that require empty-stomach dosing for proper effectiveness. Taking these with food can reduce absorption by 40% to 70%.
The Bottom Line
PO means “by mouth” — the simplest and most common way to take medication. It appears on virtually every outpatient prescription and hospital medication order, specifying that the drug should be swallowed rather than injected, applied topically, or given by another route. Understanding PO and related route abbreviations helps you take your medications correctly, verify your prescription labels, and communicate effectively with your healthcare team. When in doubt about any abbreviation on a prescription, your pharmacist can translate medical shorthand into clear, plain-language instructions in seconds.