Innovative interventions that address the social determinants of health are required to help reduce persistent health inequalities. We argue that microcredit can act in this way and develop a conceptual framework from which to examine this. In seeking to evaluate microcredit this way we then examine how randomized controlled trials, currently considered as the gold standard' in impact evaluations of microcredit, compare with developments in thinking about study design in public health. This leads us to challenge the notion of trials as the apparent gold standard for microcredit evaluations and contend that the pursuit of trial-based evidence alone may be hampering the production of relevant evidence on microcredit's public health (and other wider) impacts. In doing so, we introduce new insights into the global debate on microfinance impact evaluation, related to ethical issues in staging randomized controlled trials, and propose innovations on complementary methods for use in the evaluation of complex interventions.