hi allyson, thanks for your query, vyvanse (lisdexamfetamine) drug has got lots of side effects..any drug will produce side effects for that matter..nothing to worry.. your blood pressure is slightly under low range..your heart rate may increase because of low blood pressure also..moreover vyvanse drug itself has got side effects of producing uneven or high heart beats...if your heart beat is always in higher range better consult your physician...i given below certain important side effects of vyvanse...it is categorised into severe and less severe side effects.. severe side effects::: Get emergency medical help if you have any of these signs of an allergic reaction to Vyvanse: gives; difficulty breathing; swelling of your face, lips, tongue, or throat. Stop using this medication and call your doctor at once if you have a serious side effect such as: fast, pounding, or uneven heartbeats; decreased blood pressure (feeling light-headed, fainting); tremor, restlessness, hallucinations, unusual behavior, or motor tics (muscle twitches); or dangerously high blood pressure (severe headache, blurred vision, buzzing in your ears, anxiety, confusion, chest pain, shortness of breath, seizure). Less serious Vyvanse side effects may include: loss of appetite, weight loss; sleep problems (insomnia); nausea, vomiting, stomach pain; feeling irritable; mild skin rash; or dry mouth or an unpleasant taste in your mouth. thank you, wish u for good health, DR.PRATHAP.B