Black medicine represents the most problematic configuration of informal payments for health care. According to the accepted economic explanations, we would not expect to find black medicine in a system with a developed private service. Using Israel as a case study, we suggest an alternative yet a complimentary explanation for the emergence of black medicine in public health care systems - even though citizens do have the formal option to use private channels. We claim that when regulation is weak and political culture is based on 'do it yourself' strategies, which meant to solve immediate problems, blurring the boundaries between public and private health care services may only reduce public trust and in turn, contribute to the emergence of black medicine. We used a combined quantitative and qualitative methodology to support our claim. Statistical analysis of the results suggested that the only variable significantly associated with the use of black medicine was trust in the health care system. The higher the respondents' level of trust in the health care system, the lower the rate of the use of black medicine. Qualitatively, interviewee emphasized the relation between the blurred boundaries between public and private health care and the use of black medicine.