| Microgram | |
|---|---|
 Anutrition facts label displaying, for example, the amount offolic acid in micrograms | |
| General information | |
| Unit system | SI |
| Unit of | mass |
| Symbol | μg |
In themetric system, amicrogram ormicrogramme is aunit ofmass equal to one millionth (1×10−6) of agram. Two different abbreviations are commonly used. TheInternational System of Units (SI) usesμg, where theSI prefix "micro-" is represented by the Greek letterμ (mu). The abbreviationmcg is preferred for medical information in the United States (US), but prescription writing guidance in the United Kingdom advises that "microgram" should not be abbreviated.[1] A third abbreviation, the Greek letterγ (gamma), is no longer recommended.[2]The USInstitute for Safe Medication Practices (ISMP) and the USFood and Drug Administration (FDA) recommend that mcg should be used, rather than μg, when communicating medical information.[3] This is due to the risk thatμ might be misread asm, for "milli-", which is equal to one thousandth (1×10−3). Such a misreading could result in a thousandfoldoverdose of a drug or medicine. However, mcg is also the symbol for the obsolete unit millicentigram, derived from thecentimetre–gram–second system of units and equal to 10 μg.
Usually, a sequence of theUnicode code pointU+03BC μGREEK SMALL LETTER MU followed by the Latin letterU+0067 gLATIN SMALL LETTER G should be used. However, if μ is not available itmay be represented withU+0075 uLATIN SMALL LETTER U or the legacy Unicode symbolU+00B5 µMICRO SIGN. InChinese, Japanese and Korean writing afullwidth versionU+338D ㎍SQUARE MU G should be used.[4]
