There are several differences between Aromasin and Arimidex, the most notable of which is that Aromasin is a suicide inhibitor while Arimidex is a reversible inhibitor. This means that Aromasin permanently binds to the aromatase enzyme, while Arimidex only binds for a short period. As a result, Aromasin is less likely to cause resistance, while Arimidex may be more likely to cause resistance over time. Aromasin is also a stronger inhibitor than Arimidex and is effective at lower doses. Arimidex is more potent at higher doses. Finally, Aromasin is more effective than Arimidex at preventing gynecomastia.