Ok I was thinking his meds sounded a little wimpy. I get percocet for a toothache. He's got a lot more going on than a toothache. I forgot about the scale. That is great! 1-10 Thanks Gary.
How do you know what is too much? I want him to have his pain under control, but I don't want him to OD doing it.

That's why pain has to be managed by a doctor. The doctors actually have formulas ("titration" I believe they call them) for safely increasing the dose rate(s).

For safety they will never increase Duragesic more than 25 mcg at a time.

Read the instructions that come with the meds or talk to the pharmacist or PA. Typically respiration will be depressed and there will be other symptoms of OD. Balance this out with it takes a little time to adjust to changes in pain meds.

If it gives you any comfort factor most drugs are tested to find out what the theoretical fatal dose (on animals obviously) would be then scaled back X10 for safety reasons. This is just a general rule. I am sure that some drugs are given at dangerous levels like some chemotherapy treatments. It's all about the risk and benefit as well.