Hmm, well to recommended dose is between 200 to 400mgs, every 4 to 6 hours, for an adult. I personally usually take 400mg, every 5ish hours, but i used to take it a lot more than that, like 600mg every 4hrs, which caused me to have rebound headaches. Your body gives you signals that you are taking too much, usually. this site seems good. i haven’t read it all.. “The toxicity of ibuprofen overdose is dependent upon the amount of drug ingested and the time elapsed since ingestion, though individual response may vary, which makes it necessary to evaluate each case individually.” It depends on the person, their weight, and the last time they took it. I think they go by symptoms and if you have been taking an excessive amount, that it builds up.