I was just prescribed prozac 20mg a week ago and now my doctor added vyvanse (lisdexamfetamine) 40mg starting tomorrow. reading about serotonin syndrome - is this safe?

Caution advised: Being aware of potential side effects is definitely important. I also notice you are on Adderall (dextroamphetamine and racemic amphetamine). If these are all prescribed by same doc I am sure there is a reason for this, but if not you should always make sure any doc you see is aware of everything you take including non-prescription. You should also be commended for your use of Healthtap as a resource of trusted medical advice