What are the differences between Loewe, Bliss, and HSA, and which model are you using?

In general there are two synergy ‘Schools of Thought’: Bliss additivity and Loewe additivity. The first uses %-effects and the other focuses on dosage. This is explained well by Foucquier and Guedj (2015). ‘HSA’, highest-single-agent, also uses %-effect, but very simply takes the most potent compound as a reference. We do not use this. We base our calculations on Loewe additivity and use the isobologram and the Chou-Talalay CI Index as ways to visualize and quantify synergistic effects.