The mole is a base unit for a dose (or amount) of drug.
A mole of drug weighs in grams the same as the relative molecular mass (RMM).
For example, the RMM for NaCl is 58.45 (Atomic weight of Sodium is 23, and Chloride is 35.45).
Therefore 1 mole of NaCl weighs 58.45grams.
(You would normally be given the RMM value. However, it is important that you recognise the relationship of this value to weight of the drug in grams)