Ive been on 70mg of Vyvanse for about 4 months now after being on 60mg for over a year. I'm starting to feel like the Vyvanse isn't as effective as it use to be for me. I'm starting to bounce back and forth between my job tasks again with focusing difficulty and feeling like my brain can't think and make a decision on stuff. Is it possible for the medicine to not work after being on it. I've been on Vyvanse overall for over 3 years now.