You can safely take up to 800mg every 8 hours, but I don't recommend taking that much. Take the smallest dose that provides you with relief. The most important thing you must do is TAKE IT WITH FOOD! Or you'll end up like me... I have stomach ulcers from too much Motrin use. I've taken it for years for back pain, and didn't always eat with it. Now I'm dependent on drugs like Pepcid and Nexium to keep my stomach from hurting because the Motrin tore up my stomach lining. It's not intended for long term use... (I had been taking it for over 8 years.) So just be careful. It's also safe to alternate with Tylenol for better pain control. (Tylenol is safe on your stomach.) When I'm hurting, I'll take 800mg Motrin every 8 hrs, and Tylenol 650mg every 4 hrs. That way you get pain relief around the clock.