Ionization potentials of adenine in the vertical spectrum and along the main internal conversion pathways are computed with several high-level methods and an assessment of the quality of these calculations is provided. A long-standing divergence between experimental and theoretical results, concerning the assignment of the surface on which adenine relaxes, is reviewed based on these calculations. Ionization energy variations up to 4.5 eV between the Franck-Condon region and the conical intersections were found, with general implications for pump-probe experiments with organic molecules. The ionization potentials computed along the reaction pathways can be used as a general guide for aiding the setup and analysis of further experiments with adenine and other heterocycles.