In the metric system, a microgram (µg or mcg) is a unit of mass equal to one millionth (1/1,000,000) of a gram (1 × 10−6), or 1/1000 of a milligram. It is one of the smallest units of mass (or weight) used in a macroscopic context. The symbol "µg" (mu-g) conforms to the International System of Units and is often used in scientific literature, but the United States-based JCAHO recommends that hospitals do not use this symbol in handwritten orders due to the risk that the symbol µ might be misread as the prefix m, resulting in a thousandfold overdose. The abbreviation mcg is recommended instead.
See also 
- "ISMP's List of Error-Prone Abbreviations, Symbols, and Dose Designations". ISMP. Retrieved 2011-11-02.