In illicit drug markets, the price and purity of drugs change frequently. While it is well known that purity-adjusted price affects drug use, impacts on other outcomes are less clear. This rapid review examines the relationship between price, purity and seven population level measures of drug-related harm and any differences across three drug types. With a few exceptions, it found an inverse relationship between purity-adjusted price and drug-related harm, with higher purity-adjusted price associated with less drug-related harm, and lower purity-adjusted price associated with increased harm. This shows the value of price and purity data for predicting drug market impacts and the importance of improving price and purity data collection and analyses, particularly in Australia.