Adhd stimulants throw up bile?

i just went back on my concerta (essentially a ritalin xr ) and i have lost my appetite. i have experienced a decrease in appetite however i still think i am consuming around at least a 1000 calories to 1300 calories a day. ive been on it for a week and i threw up bile this morning, why did this happen? im not fat i usually eat around 2000 calories a day so this isnt a significant decrease