Last I heard tamoxifen was on customs banned substance list. I've slipped banned substances through customs before after returning from Mexico. If they do figure out what it is, they'll just take it from you. A lot of times though they don't even seem to know what the hell you have and as long as they know that it's not a controlled substance, they'll let you keep it under the "3 month personal supply" rule. When they ask you about it, tell them it's a treatment for a relatives breast cancer. Just say that you were able to get it at a much better price in Egypt. Don't try to hide it though. It doesn't matter what it is, if you try to hide it, it really pisses 'em off.