They are. The first time you have your prescriptions filled through a retail pharmacy locally you'll receive a letter in the mail from Express Scripts telling you to move your prescriptions to the online pharmacy and how to go about it. I believe you have 2 refills before you'll start paying a higher copay for maintenance medication (Spiro, Progesterone, etc). The price difference isn't exceedingly high, but it's noticeable if you're on a tight budget.
It's a relatively simple process and can be done through the express scripts site. PM me if you have any specific questions.
