This paper critically appraises the current evidence as to whether social prescribing reduces the demand for health services and is cost effective. It draws on the results of a systematic review of online databases which identified 94 reports, 14 of which met the selection criteria. They included studies on the effect of social prescribing on demand for general practice, the effect on attendance at accident and emergency (A&E) and value for money and social return on investment assessments. The evidence broadly supports the potential for social prescribing to reduce demand on primary and secondary care, however, the quality of the evidence is weak. It also identifies encouraging evidence that social prescribing delivers cost savings to the health service, but this is not proven or fully quantified. In conclusion, the paper looks at the possible reasons for the growth in scale and scope of social prescribing across the UK and makes recommendations for more evaluations of on-going projects to assess the effectiveness of social prescribing.