A gastrointestinal implant system includes an adjustable restriction device having a contact surface configured for at least partially engaging a surface of a gastrointestinal tract of a mammal. The implant system further includes an implantable interface including a first driving element, the first driving element being moveable and operatively coupled to the adjustable restriction device by an actuator configured to change the dimension or configuration of the contact surface in response to movement of the first driving element. The system also includes an external adjustment device having a second driving element configured to non-invasively engage the first driving element of the implantable interface from a location external to the mammal. In the system, actuation of the second driving element of the external adjustment device produces movement in the first driving element of the implantable interface and results in a change in the dimension or configuration of the contact surface.