Can you take Zyrtec and Vyvanse?

Zyrtec (cetirizine) and Vyvanse (lisdexamfetamine) have no known major drug to drug interactions, and can be taken safely together. However this combination may cause a increased sedating effect, so until you know how severe this effect is; you shouldn't operate a vehicle/heavy machinery because you could fall asleep at the wheel.

Of course I must insist that you clear this answer with a physician and/or a primary healthcare provider.