Objective To evaluate how decision-support resources about taking up or interpreting genetic testing for hereditary cancer predispositions are experienced, and impact on cognitive or emotional outcomes. Methods A systematic review of quantitative, qualitative and mixed-methods studies involving adults with or without cancer who used an intervention to inform decisions about any cancer susceptibility genetic test or screening/risk-reducing options due to a known pathogenic gene variant. Interventions could be digital or paper-based and included information, education, risk presentation and decision-support resources. Study findings were summarised using narrative synthesis. Results Thirty-six publications describing 27 interventions were included. Interventions had a positive impact on experience and cognitive, emotional, and behavioural outcomes. None appeared to cause harm. Conclusions Decision-support resources should be used to complement the cancer genetic counselling patient pathway. These should be rigorously developed according to evidence-based frameworks and in collaboration with patients.