The internet has given rise to an informational landscape that challenges epistemological hierarchies between experts and lay people. Tensions regarding how to address the growing flora of counter-authority claims are pertinent in the context of health, where warnings about misinformation co-exist with notions of patient empowerment. This context accentuates the importance of revitalizing conceptualizations of how to assess the validity of knowledge claims. In this article, we put critical realist discussions on judgemental rationality into conversation with the case of a group of women who claim that the contraceptive copper IUD may lead to side effects of a kind not recognized by medical authorities. Tracing our own path from radical uncertainty to regarding the women’s claims as a plausible hypothesis, we identify what we deem to be strengths and weaknesses of the women’s claims and pinpoint the judgementally rational grounds for this assessment.