If my friend took around more than 1,600mg of ibuprofen at once a day ago and is below 105 pounds, should she go to the e.r?

NO: First of all it's a day later and nothing can be done Secon and most important 800mgm every 8 hours is the therapeutic dose (Prescription dosage NOT OTC)so 2400 mgm is therapeutic. Outside of possible STOMACH irritation there is nothing dangerous about your friend's situation! Hope this helps ! Dr Z

Yes, but ...: She weighs about 48 kilograms. She took a dose of 1600/48 = 33.3 mg/kg which is three times the usual dose. The best thing to do in the US is call Poison Control. The phone company has set aside the number POISONS in all area codes so you don't have to look it up, just like 911 as a number to call police or fire.