Forests are under increasing pressure globally and the establishment of protected areas has long been used as a conservation tool to preserve them. Seven categories of protected areas have been defined by the International Union for Conservation of Nature (IUCN) with different management objectives and protection levels. However, recent studies raised questions over whether protected areas are effective in preventing ecosystem degradation and whether IUCN categories vary in their effectiveness. In this study, we analysed forest loss and trends between 2001 and 2014 within IUCN protected areas at a global scale and within sixteen Intergovernmental Platform for Biodiversity and Ecosystem services (IPBES) subregions, relevant for international policy. As habitat protection can be driven by the location of protected areas and as the amount of forest within protected sites is highly unequal, we reported the forest loss integrating the proximity of roads and population, as well as the amount of initial forest in 2000. Our results show that worldwide, the highest protection categories experienced less forest loss than those allowing more human intervention, although this result was reversed in three IPBES subregions. Moreover, in four subregions there was more forest loss within protected areas than outside. We also found accelerating rates of forest loss in protected areas across all IUCN categories, more pronounced in the highest protection IUCN categories. Our results highlight the importance of moving the discussion of the post-2020 biodiversity framework for protected areas beyond simple general areal targets and that areas with poor implementation effectiveness should benefit from additional support.