If I normally take 30 mg of vyvanse, (lisdexamfetamine) will it be safe to switch to 20 mg adderall?

Roughly, a dose . of Vyvanse (lisdexamfetamine) = about 3 times a dose of Adderall XR. 30 mg. of Vyvanse (lisdexamfetamine) or ~10 mg. of Adderall XR is a low daily dose for an adult. Starting at15 mg. of Adderall XR & titrating up under your psychiatrist's guidance to optimal effect without side effects may be more tolerable. You may find Adderall XR to have quicker onset & shorter duration of action; irritability may occur as the dose is increased. .