I think if they were looking for drugs they would check incoming international flights when the passengers got off.
The body scanners are only used for passenger on outgoing flights? I hadn't considered that was the case. It might not be a bad idea to have some security checks on incoming flights from countries that have lax or suspect security but I'm still puzzled as to why, as far as I know, only one country uses x-ray scanners. Pakistan would be on my list right now!