actually equivalent for doses of ibuprofen at 400, 600, and 800 mg. So a lot of doctors and healthcare organizations decided to get rid of the 800 mg dose, and only give 600 mg to big adults, and everybody else max out at 400 mg. The idea being that most people receive the same level of pain relief with 400 mg, but with half the medication toxicity.
This article from 2008 talks about it: