Aromasin does take longer to work than Arimidex. So if you're the person that waits for estrogen sides to show up THEN start taking Aromasin it can take another week or two for it to catch up. That's why it's important to start from the beginning of the cycle. In this emergency situation Arimidex would be the better choice because it will work faster. Aromasin should ALWAYS be used in PCT to prevent estrogen rebound even if Arimidex was used during cycle. If you're on TRT it doesn't really matter the choice is up to you but generally Aromasin is better with less sides on lipids.