Hospital papers
What Does Nil by Mouth Mean?
Nil by mouth · say it: NIL by MOWTHAlso written: NBM, NPO, nil per os, nothing by mouth, fasting before a procedure
Short answer
Nil by mouth means a person should not eat or drink anything, usually before surgery, a procedure or certain tests.
What it means
Nil by mouth (NBM), also called NPO from the Latin "nil per os", is an instruction not to eat or drink. It is often used before an anaesthetic, sedation, surgery or some scans.
It is mainly a safety measure. An empty stomach lowers the risk of stomach contents getting into the lungs during anaesthesia or sedation. It can also be used when someone has trouble swallowing safely or has certain gut problems.
The exact rules, such as how long before and whether small sips of water or regular medicines are allowed, differ between hospitals and procedures. Always follow the instructions you were given. The phrase is sometimes heard or typed as "mil by mouth" or "nill by mouth"; it is the same instruction. Its opposite on a chart is PO, which means a medicine is given by mouth.
Where you may see it
- Hospital notes and bedside signs
- Pre-operative instructions and appointment letters
- Ward handover notes
📄 How it looks on a report
NBM from midnight for theatre.
🙅 What it does not mean
- It does not always mean stopping all medicines. Ask whether to take your usual medicines.
- It is not a punishment or a sign something has gone wrong. It is a routine safety step.
- It is not the same as a fasting blood test, which has its own instructions.
🗒️ Questions to ask your doctor
🧾 Reports where you will see “Nil by mouth”
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🔗 Read more from trusted sources
- “Nil by mouth” on MedlinePlus ↗
US National Library of Medicine
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General information about a medical word, not advice about your own results. Ask the clinician who ordered the test what it means for you.