In the metric system, a microgram (µg; or sometimes: mcg) is a unit of mass equal to one millionth (1/1,000,000 or 1×10−6) of a gram, or one thousandth (1/1000 or 1×10−3) of a milligram. The unit symbol is µg according to the International System of Units. In µg the prefix symbol for micro- is the Greek letter µ.
The United States-based Joint Commission recommends that hospitals do not use the symbol µg in handwritten orders 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.
- "ISMP's List of Error-Prone Abbreviations, Symbols, and Dose Designations". ISMP. Retrieved 2011-11-02.