I did your example:
Controller:
function medicine()
{
$crud = new grocery_CRUD();
$crud->set_table('tbl_patient_medicine');
$crud->required_fields('id_patient','name_medicine','dosis','start_date','treatment','time_per_day');
$crud->columns('id_patient','name_medicine','dosis','start_date','treatment','time_per_day');
$crud->fields('id_patient','name_medicine','dosis','start_date','treatment','time_per_day');
$crud->set_relation('id_patient','tbl_patient','name');
$output = $crud->render();
$this->_example_output($output);
}
It works!
Edited:
$crud->set_relation('id_patient','tbl_patient','{name}, {att1}, {att2}, {att3}');