Background: Nowadays, a growing literature reveals how patients use informal payments to seek either better treatment or additional services, but little systematic review has been accomplished for synthesizing the main factors. The purpose of this study was to analyze the content of literatures to demonstrate the factors for informal patient payments. Methods: In this systematic review study, PubMed, Web of Science, Wiley Online Library, Science Direct, Ovid, Scopus, and Iranian databases were investigated without time limitation for eligible English and Persian studies. Achieved data were analyzed using content analysis approach and MAXQDA 10 software. Results: Themes related to informal payments in external context of health system were demographic features of health service consumers, patient's personality features and social & cultural backgrounds of the community. Health system challenges' themes were about stewardship weakness, and sustainable financing and social protection weakness. These were followed by human resources' organizational behavior challenges, drugs, medical products, and services delivery provision process challenges and finally change management weakness for reducing and dealing with IPs. Conclusion: It appears that improving the quality of health care services and accurate monitoring of delivery processes, along with performing some strategies for regulating payroll and medical tariffs, strict rules and regulations and improving health staff motivation, would be effective ways against informal payments. Improving the health insurance contribution, promoting transparency & accountability in health system especially in financing, identify precise control mechanism, using empower patient/public related approach, modifying community perception, reinforcing social resistance to unofficial payments and rebuilt lost social capital in health care are some of the other recommendations in this field. To practice these strategies, a comprehensive and systemic vision and approach is needed, however, the key point is that before applying any strategy the impact of this strategy on access, efficiency, equity, and other health systems' goals and policies should be investigated due to the consideration.