How do you know when your taking too much methadone?

When you feel comfortable, but not high. And of course the most important thing is when you do not crave any other opiate. The point of methadone maintenance is to stabilize your lifestyle so that you can function in society while getting treatment and recovering from addiction. If you are coming home, eating and passing out, you are on too high of a dose. You should not have to go higher than 120 mg's unless you have really high metabolism, but methadone actually slows your metabolism so eventually your dose will start feeling stronger and stronger before finally stabilizing.