<s>[INST] I have been on Prozac for 8 days and have lost 6 pounds already. I have been on Vyvanse for about 6 years now, and now take Vyvanse and prozac together and it just seems like I m not hungry at all ever. I have to force myself to eat. Why is this? I am on Vyvanse 50 mg not instead of 70mg and on Prozac at 20mg. [/INST] Hi , prozac can increase the effects of vyvanse and can cause serious side effects like anxiety and jitteriness.Serious interaction called serotonin syndrome can occur . So these drugs should not be taken together.Thanks </s>