Subtle difference in the units.
Definitions:
Milligram: A unit of measurement of mass in the metric system equal to a thousandth of a gram. 1mg means 0.001 of a gram
Microgram: A unit of measurement of mass in the metric system equal to a millionth of a gram. 1 mcg means 0.000001 of a gram. It is more usual to write μg for micrograms.
And as Sepp says 2000 micrograms = 2milligrams.
