Common ragweed (Ambrosia artemisiifolia) is a neophyte from North America that has spread rapidly throughout Europe. Because the pollen of common ragweed is highly allergic, many countries have adopted containment and mitigation measures. The neophyte has only recently established flowering populations in Sweden. We use this well documented case to study the early impacts of an invasive species on human health. Our identification strategy relies on spatial and temporal variation in common ragweed populations and health data for 1998-2011, applying panel-data estimation techniques. To ensure the robustness of our findings, we test and correct for heteroskedasticity and autocorrelation. Our estimates show that an invasive species still in its lag phase can yet have adverse impacts on human health.