What is the minimum dose of ethinyl estradiol in OC pills for contraceptive effect?

For the average patient, the first choice of preparation for contraceptive purposes is a very low estrogen OC (20 mg EE) unless there are other considerations, for example, previous pregnancy while taking the pill.Patients with persistent break-through spotting or bleeding could be offered a pill with the same low estrogen dose, but a more potent progestin, for example, levonorgestrel.Ref: Reference: Novak's gynaecology; 14th edition; Chapter 10; Family planning