A new study published in Drug and Alcohol Dependence by researchers from Yale University reports that Google Maps is currently the most reliable way to identify marijuana dispensaries nationwide, outperforming state regulatory lists and popular industry directories.

The research team set out to solve a longstanding problem: there’s no single comprehensive source for dispensary locations, making it difficult to accurately measure how retail availability affects marijuana use, access, and public health outcomes. To test what works best, the researchers gathered dispensary listings from Google Maps, Weedmaps, Potguide, RefUSA, and state regulatory agencies. They then called every dispensary across selected zip codes in legal marijuana states to verify whether the businesses were real and operating.

Google Maps identified the highest number of dispensaries and showed the strongest sensitivity at 96%. It also flagged the most potentially unlicensed shops, a reflection of how quickly its listings capture on-the-ground activity. The platform’s accuracy improved even further when researchers removed listings marked as closed or those without phone numbers, pushing its positive predictive value to more than 96%.

Other sources were far less complete. Weedmaps had the highest proportion of verified listings but identified less than half as many dispensaries as Google Maps. RefUSA included historical data but was significantly less accurate, and state licensing lists missed many operational stores and, by definition, excluded unlicensed ones.

The study found no meaningful differences in accuracy between rural and urban areas, an important factor for nationwide research. The authors say the findings show Google Maps is currently the strongest single resource for cross-sectional dispensary mapping, especially when paired with basic filters to remove closed or unverifiable listings.