In this paper, the analytical and computational theory of quasi-linear and toroidal effects on electron cyclotron current drive (ECCD) is presented. Simple analytical formulae for the estimation of the ECCD correction due to the action of high-power microwaves and banana electrons are obtained. The article extends the results of calculations performed with the use of the OGRAY code. Good agreement between the analytical and numerical calculations is obtained. The optimum conditions of ECCD are investigated.