The MG medical abbreviation has three common meanings: mg in lower case is a milligram, a unit of weight used for medicine doses; Mg with a capital M is the chemical symbol for magnesium, a mineral measured in blood tests; and MG in capitals usually means myasthenia gravis, a nerve and muscle condition.
Letter case is the first clue, but it is not always reliable, since some systems print everything in capitals. The words around the abbreviation settle it. This guide walks through each meaning, how a magnesium level is read, and a safety rule that applies when magnesium sulfate is written in shorthand.
At a glance
Stands for
Milligram (mg), one thousandth of a gramOther meanings
Magnesium (Mg); myasthenia gravis (MG)Written as
mg for the unit, Mg for the element, MG for the conditionNormal range
Blood magnesium often about 1.7 to 2.2 mg/dL; labs varySafer to write
Magnesium sulfate in full, not MgSO4Do not confuse with
mcg (microgram), a unit 1,000 times smaller
Telling the three meanings apart
| Written | Meaning | Typical setting |
|---|---|---|
| mg | Milligram | Prescriptions, medication labels, lab units such as mg/dL |
| Mg | Magnesium | Electrolyte panels, ICU and cardiac notes |
| MG | Myasthenia gravis | Neurology notes, problem lists |
A dose such as 500 mg is always the unit. A line that reads Mg 1.9 alongside potassium and calcium is the mineral. A problem list entry like "MG, on pyridostigmine" points to the condition. If none of these clues fit, check with the author of the entry.
Milligrams on labels and orders
On a prescription, mg tells you the strength of each dose, as in metformin 500 mg. It also appears in lab units: mg/dL means milligrams per deciliter of blood. The unit that causes trouble is the microgram, written mcg. One milligram equals 1,000 micrograms, so a mix-up between the two changes a dose a thousandfold.
Safety groups advise writing mcg rather than the Greek letter mu, and never adding a trailing zero after a whole number, such as 5.0 mg, which can be read as 50 mg. The prescription and dosing shorthand guide covers other units and timings.
Magnesium as a lab test
Magnesium helps muscles, nerves and heart rhythm work properly. A serum magnesium test is often drawn with other electrolytes in hospital, especially in people with heart rhythm problems, poor intake, heavy alcohol use, diarrhea or kidney disease, and in those taking certain diuretics or acid-reducing medicines.
Many labs use an adult range of about 1.7 to 2.2 mg/dL, while some report in mmol/L. Your report shows its own range.
Nursing handoff: "Mg 1.4 this morning, replacement running, recheck with evening labs." The magnesium was below range, a supplement was being given through the IV, and the level would be checked again later.
Mg medical abbreviation safety and MgSO4
The Joint Commission includes MgSO4 among its do-not-use abbreviations, grouped with MS and MSO4. The concern is that MgSO4 and MSO4 can be mistaken for each other, and MSO4 was used for morphine sulfate. Confusing the two could lead to the wrong drug being given.
The safer form is to write magnesium sulfate and morphine sulfate in full. Many order systems now block the short forms. If you see MgSO4 on an older handwritten record, ask a pharmacist or nurse to verify the intended drug. See the MS abbreviation page for the morphine side of the mix-up.
Myasthenia gravis in neurology notes
Myasthenia gravis is an autoimmune condition in which the signal between nerves and muscles is blocked, leading to muscle weakness that worsens with use and improves with rest. Drooping eyelids and double vision are common early signs. Neurologists may write MG in the history, the assessment and the problem list, and terms such as AChR antibody or myasthenic crisis are clues that MG means the condition.
MG medical terminology for students
In charting, keep units in lower case (mg), use Mg only next to other electrolytes, and spell out myasthenia gravis the first time in a note. Spell out magnesium sulfate in every order. The guide to lab and test abbreviations links related electrolyte terms.
This page explains abbreviations only. Any question about your own dose, magnesium level or diagnosis is best taken to your pharmacist, nurse or doctor.
Frequently asked questions
What does mg mean on a prescription?
It means milligram, the weight of the medicine in each dose. A label showing 10 mg means each tablet or dose contains ten milligrams of the drug.
What does Mg mean on a blood test?
Mg is the symbol for magnesium, a mineral checked with other electrolytes. The result is usually given in mg/dL or mmol/L with the lab's reference range beside it.
Is mg the same as mcg?
No. A microgram (mcg) is one thousandth of a milligram. Mixing them up can change a dose a thousandfold, so safety groups want the microgram unit spelled as mcg.
Why should MgSO4 not be written?
It can be confused with MSO4, a shorthand once used for morphine sulfate. Both appear among The Joint Commission banned abbreviations, so magnesium sulfate is spelled out.
What does MG mean in a neurology note?
In neurology MG usually means myasthenia gravis, a condition causing muscle weakness that worsens with activity. Clues include antibody tests, eyelid drooping and double vision.