The effect of hormonal oral contraceptives (OCs) on carbohydrate metabolism depends on the amount of estrogen (ethinyl estradiol or mestranol), type and amount of progestin, formulation of the pill (monophasic, sequential, or triphasic), duration of use, mode of administration (oral v parenteral), and race and genetic predisposition of the user. The progestin megestrol has minimal effect on carbohydrate metabolism but is no longer available due to its carcinogenic effects in beagle dogs. Combination pills with norethindrone and its derivatives (norethindrone acetate, norethynodrel, and ethynodiol diacetate) show moderate impairment of glucose tolerance with definite hyperinsulinemia. The lowest metabolic effect was observed with triphasic formulations. The effect of levonorgestrel depends on the formulation; the highest impairment of glucose and insulin response after oral glucose loading is found in sequential and combined formulations with doses of 50 micrograms ethinyl estradiol, whereas with doses of 30 micrograms ethinyl estradiol only minor effects on glucose tolerance are seen. Few effects were observed while using triphasic preparations. Therefore, to minimize disturbances of carbohydrate metabolism, low-dose formulations and triphasic preparations should be used.