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The latter is most likely due, at least in part, to differences in intrinsic characteristics of participants. We find that major impediments to clear conclusions on these topics include a lack of standardized methodologies, comparisons between non-parallel clinical studies and variability of data on serum concentrations between and within studies. We show that there is a paucity of research on most of these topics for most progestins. Here we review the current knowledge on these topics and identify the research gaps.
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This requires a better understanding of the pharmacokinetics, metabolism, serum and tissue concentrations of progestins used in contraception as well as the biological activities of progestins and their metabolites via steroid receptors. There is a need to develop new methods to suit different needs and with minimal risks, especially in under-resourced areas. There is an increasing awareness that different forms of contraception and different progestins have different side-effect profiles, in particular their cardiovascular effects, effects on reproductive cancers and susceptibility to infectious diseases. These contraceptives differ in the dose and type of synthetic progestogenic compound (progestin) used, as well as the route of administration and whether or not they contain estrogenic compounds. Many different forms of hormonal contraception are used by millions of women worldwide.
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