In the metric system, a microgram or microgramme is a unit of mass equal to one millionth (1×10−6) of a gram. The unit symbol is μg according to the International System of Units; the recommended symbol in the United States when communicating medical information is mcg. In μg the prefix symbol for micro- is the Greek letter μ (Mu).
Abbreviation and symbol confusion
When the Greek lowercase “μ” (Mu) in the symbol μg is typographically unavailable, it is occasionally—although not properly—replaced by the Latin lowercase “u”.
The United States-based Institute for Safe Medication Practices (ISMP) and the U.S. Food and Drug Administration (FDA) recommend that the symbol μg should not be used when communicating medical information due to the risk that the prefix μ (micro-) might be misread as the prefix m (milli-), resulting in a thousandfold overdose. The non-SI symbol mcg is recommended instead. However, the abbreviation mcg is also the symbol for an obsolete CGS unit of measure known as millicentigram, which is equal to 10 μg.
In the UK, the μg symbol is the widely recognized method of identifying micrograms.
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- List of SI prefixes
- Orders of magnitude (mass), listing a few items that have a mass of around 1 μg.
- "ISMP's List of Error-Prone Abbreviations, Symbols, and Dose Designations". ISMP. Retrieved 2018-03-28.
- "List of UK NHS Dose Designations". NHS. Retrieved 2018-12-28.
- NIST Handbook 133 - 2018, Appendix E. General Tables of Units of Measurement, page 159 (17)
- Unicode Consortium (2019). "The Unicode Standard 12.0 – CJK Compatibility ❰ Range: 3300—33FF ❱" (PDF). Unicode.org. Retrieved May 24, 2019.