stimulant medications are known to either lose weight or gain weight. if you lost weight on concerta, you may also lose on vyvance, although i have no tried vyvance. I lost my appetite when on concerta though. I am 5'6 and weight 120. That is in the ok range I think. The key is to eat healthy snacks (if it is too overwhelming to eat a whole meal) that are full of protien and nutrients. Try a protein smoothie or a granola bar or a pbj.

If you have a fast metabolism (which i certainly do), the med may go through you faster, and not last as long. But it really depends. For me, I was on extended release concerta which is suposed to last 8-12hours I think, and it was gone and out in about 5 for me. Again, never tried vyvance so I can't tell you anything about that.