The effects of losses of the fast electron current carriers are included in a calculation of the efficiency of RF current drive. The analytical expressions obtained for the current drive efficiency J/PA and bulk heating rate PD/PA are explicitly dependent on the fast electron confinement time, TF. In most present tokamak experiments, fast particle losses are predicted to reduce the current drive efficiency from 50% to more than an order of magnitude. However, in future fusion plasmas fast electron confinement appears to be sufficient to allow nearly ideal efficiencies to be achieved.