Name a study or provide a link that confirms that the body can only use a certain amount of pain medicine?

Question

i.e. Does taking 3 Advil any different from taking 6

Answer 1

No study to quote or a link...but there is the real fact of overdose to consider. More is not always better. you can take to much. It would appear to be logical that this is a gradual process and not one that makes a tremendous leap.

Answer 2

I don't know the name of the study, but OTC pain relievers have a ceiling effect. Any amount above a certain level produces more side effects and no additional analgesia.
For Tylenol (acetaminophen, paracetamol), this occurs above 1000-1250mg. But Tylenol is very hepatotoxic at high doses. The toxic level is 4 grams (4000mg) per day and he LD50 is between 8-10 grams (8000-10000 mg) per day.
In Advil (ibuprophen), the ceiling is between 800-1000 mg However, at higher doses, gastrointestinal bleeding can occur. And, Advil at excessive doses (about 2 grams) is also toxic for the liver and kidneys.
For opioids, the ceiling effect usually does not occur. This is more true for pure agonists (eg. morphine, oxycodone, hydromorphone). The only limit is the side effects. This is usually respiratory depression. Codeine has a ceiling at about 250 mg. Butorphanol has a ceiling at about 4-5 mg.