vyavanse (lisdexamfetamine) is a cns stimulant with major side effects being insomnia (lack of sleep) and abuse potential. It can also cause other effects like dryness of mouth and increase in heart rate. However, there are no documented side effects of derranged blood sugars with this drug. I think you should recheck your dietary and drug compliance . Also, if there has been a change in your daily lifestyle ( changed timing of meals, altered sleep wake cycle) , these things can alter fasting blood sugars. Lastly, it would be prudent if you tell about the anti diabetic or any other medication that you are on.. to rule out a remote possibility of drug-drug interaction. Thanks