Clinical Question: Do oral contraceptives containing norethindrone acetate or levonorgestrel differ in their effect on suppression of menses with continuous use?

Setting: Population-based

Study Design: Randomized controlled trial (double-blinded)

Allocation: Concealed

Synopsis: There were 139 women enrolled in this double-blind, four-arm trial of oral contraceptives used continuously for 180 days for the purpose of suppressing menstrual periods. The estrogen used in all study arms was ethinyl estradiol (E₂), which could be at a dose of 20 mcg or 30 mcg. The progestin was 1 mg norethindrone acetate (Loestrin) or 100 mcg levonorgestrel (Seasonale). The four study arms included: (1) norethindrone acetate plus 20 mcg ethinyl E₂; (2) norethindrone acetate plus 30 mcg ethinyl E₂; (3) levonorgestrel plus 20 mcg ethinyl E₂; and (4) levonorgestrel plus 30 mcg ethinyl E₂.

All study participants had used cyclic oral contraceptives for at least three months before randomization. This study had an overall drop-out rate of 45 percent. More days of amenorrhea were recorded in the norethindrone acetate groups, with no difference between the lower versus higher estrogen dosing (mean days of amenorrhea during 180 days’ use: norethindrone acetate plus 20 mcg ethinyl E₂ = 164, levonorgestrel plus 20 mcg ethinyl E₂ = 151; P = .02).

Bottom Line: In continuous dosing regimens, more days of amenorrhea can be achieved with oral contraceptives containing 1 mg norethindrone acetate than with oral contraceptives containing 100 mcg levonorgestrel. (Level of Evidence: 2b)