We examine the negative relationship between the rate of growth in credit and the rate of growth in output per worker. Using a panel of 20 countries over 25 years, we establish that there is a robust correlation: the higher the growth rate of credit, the lower the growth rate of output per worker. We then proceed to build a model in which this relationship arises from the fact that investment projects that are more risky have a higher return. As their borrowing grows more quickly over time, entrepreneurs turn to safer, hence lower return projects, thereby reducing aggregate productivity growth. We take this theoretical prediction to industry-level data and find that credit growth disproportionately harms output per worker growth in industries that have either less tangible assets or are more R&D intensive.