While Target sold its pharmacy business in 2015, it still relies on the foot traffic generated by prescription refills to help bolster their sales. Switching your prescriptions to another store will deny Target this foot traffic.
Just visit the Target Pharmacy that holds your prescriptions and tell them you are switching your business because of Target’s same-sex bathroom and fitting room policy. Then visit the pharmacy of your choice and request the transfer. Here are links to some of the major pharmacies explaining how to make the transfer.