Can pharmacy be used as a back up to medical school?

can it if I major in biology pre-med?

It can be, but…

Pharmacy school has some additional course requirements that med school doesn’t–microbiology, human anatomy & physiology, economics, and public speaking.

(for a table of all pharmacy school requirements listed by school–http://www.aacp.org/sites/default/files/2017-11/pre_reqs-2017-18%20FINAL.pdf)

In pharmacy, chemistry is more important, while biology is secondary. If you are good in chemistry, pharmacy can be your plan B. Of course as WOWM said, the requirements are different, you need to plan for it. In addition, if you drop out of premed because of poor grade, pharmacy school will have a problem with it as well.