The World Health Organization (WHO) and international human rights bodies have long urged states to take steps to ensure that ‘conscientious objection’ does not undermine access to abortion in practice. This review uses an established methodology to identify and integrate evidence of the health and human rights impacts of the practice of conscientious objection/refusal. The evidence identified in this review suggests strongly that conscientious objection negatively affects the rights of abortion seekers and has negative implications for the rights of non-objecting health workers. This is exacerbated in situations where an exercise of ‘conscience’ goes beyond ‘opting out’ of providing care and extends into seeking to prevent abortion through dissuasion, misinformation, misdirection, delay, and sometimes abuse. The insights from this review suggest that states must take better and further action to centre abortion seekers in the regulation of conscientious objection, and to prevent and ensure accountability for rights-limiting manifestations of conscience that go beyond opting out of direct provision of abortion care in non-emergency settings.