Thank you for your question and welcome to ADHDCentral.com.   Some people have indicated that they have developed a tolerance to medication after a period of time and their dosage was either increased or they tried a different medication.   Since all people react differently to medication based on their individual metabolism, it would be impossible to say specifically why this has happened. It is possible your metabolism is different than it was several years ago based on your lifestyle and this may have an impact on how the medication is working for you.   Please talk with your doctor. He or she would be better able to determine if your medication needs to be adjusted.   Eileen