Concern about the impact of oral contraceptive (OC) use on women’s sexual functioning, particularly lowered sexual desire (or libido), has been expressed for almost as long as OCs have been available. Despite numerous studies over several decades, however, we still do not know the underlying mechanism for negative effects nor can we predict which women will suffer from them (Sanders, Graham, Bass, & Bancroft, 2001). The research has consistently produced mixed evidence, of two kinds. First, there is mixed evidence across studies: some report negative associations between desire and OC use, others find no effect, and still others report positive effects (for recent reviews, see Burrows, Basha, & Goldstein, 2012; Davis & Castano, 2004; Pastor, Holla, & Chmel, 2013; Schaffir, 2006). Second, within their respective samples, studies also consistently report considerable individual variation in women’s experience: relatively large proportions of women experience a marked increase or decrease in desire, with others unaffected (Burrows et al., 2012; Davis & Castano, 2004; Pastor et al., 2013; Schaffir, 2006). For example, in a prospective study, 17 % had a higher frequency of sexual thoughts and 39 % had a lower frequency, following initiation of OC use (Sanders et al., 2001). Understanding this mixed pattern of results would likely benefit from a meta-analytical approach, although this would need to take into account the wide variation between studies in both methodologies and OC formulations under test. Currently, on the basis of these mixed effects, researchers typically conclude that the influence of OC use on sexual desire is complex and likely due to multiple psychosocial influences (Burrows et al., 2012; Davis & Castano, 2004; Pastor et al., 2013; Schaffir, 2006). Indeed, themostrecentreviewconcludedthat‘‘wecannot define a single indicator reliably and clearly characterizing a cause-effect relationship. This is mainly due to thesimultaneous and intertwined effects of a variety of complex biological, psychological, social, and multidimensional factors’’(Pastor et al., 2013). While thismaybeanaccurate reflectionof thecurrentempirical state of affairs, it is clearly unsatisfactory both to women concerned about possible consequences for their relationships and to healthcare providers who are unclear about what advice to give. Perceived changes in libido and arousal are important contributors to OC switching and discontinuation (Sanders et al., 2001). Understanding the mechanism underpinning these mixed effects is therefore of significant public health concern and this is a matter of global importance. According to the UN report on World Contraceptive Use 2011, 9 % of partnered women of reproductive age worldwide report using OC as their main contraceptive method, rising to 18 % in some regions. In the United States, 82 % of sexually experienced women, aged 18–44 years, had used OCat some stage of their lives (Mosher&Jones,2010). Against this background, new perspectives that might help to clarify the issue should be seized upon and scrutinized carefully. The possibilities that modulatory effects on mood or reduced circulatingtestosteronelevels(e.g., throughup-regulationofsex S. C. Roberts (&) School of Natural Sciences, University of Stirling, Stirling FK9 4LA, UK e-mail: craig.roberts@stir.ac.uk
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