Side effects influence the acceptability and continuation of hormonal contraceptives. Counseling the client about the management of side effects is a principal approach advocated for increasing continuation. Evidence of a biological basis for variation in women's tolerance of hormonal contraceptives argues, however, that greater attention should be given to altering the product rather than principally attempting to alter a woman's ability to deal with the product. Discontinuation rates for hormonal contraceptives, largely attributable to side effects and health concerns, are high in nearly all less-developed countries for which Demographic and Health Survey data are available. Oral contraceptives appear to be particularly problematic for Latin American women, most notably in Bolivia. Clinical trials suggest substantial variation in the physiological response to exogenous hormones, and new evidence confirms the hypothesis that the normal hormonal profiles of Bolivian women are significantly lower than those of women in the United States. These findings suggest a need for more population-specific physiological research linked to analyses of the possible association between endogenous hormone differences and contraceptive continuation. Appropriately adjusting the level of the steroid delivered may benefit women's health and improve the acceptability and continuation of hormonal contraceptives.