Does Adderall XR stop working?

Hi, pastornack!
Although you are on a very high dose it's likely that your metabolism has become habituated to the drug. It's a mixture of two forms of amphetamines which are highly addictive even when used only as prescribed and withdrawal must be done over an extended period of time to avoid withdrawal symptoms.
You might want to talk with your doctor about your other options. There may be safer and more effective medications.