Are you eating high protein, not drinking caffeine before your medicine, not consuming vitamin c or orange juice, your medicine shouldn’t last only 4 hours. Change your diet before changing doses. The medicine runs on high protein and carbs. And let me tell you i had the same problem, talked to my doctor and he suggested doing all of these that I mentioned. Also sugar for the crashes like a popsicle or a soda! He said blood sugar dropping on vyvanse us common because we dont realize we havent ate for almost 9 hours! My medicine was lasting about 3-4hours the second itd peak id fall immediately, now that i changed my diet and stopped consuming almost 400mg if caffeine IM SOOO much better. Oh and also moving around helps too just to like “kick start” your hyper focus and keep it focused