Search of US Mail, that is sent to and originates from the US, would require a search warrant unless you are on the terrorist watch list, which I HIGHLY doubt from your posting. The following is NOT poking fun at anyone. It is a realistic worst case chain of events that would have to happen and intended to put people at ease. I appologize if I offend.

Let's play "What is the WORST case scenerio." The package was inadvertantly ripped open during delivery AND a postal employee "USPS" noticed the contents AND USPS identified the contents of the package as c-III or suspicious AND USPS contacted the authorities AND the authorities not only took the time to verify that the pills were not prescribed to you, but they also went back to the source and obtained an admission and proof that you ordered them in violation of federal law AND (this is the big one) the LE agency who did that investigation is able to find a US Attorney, because these are federal charges, who is not seriously overworked OR incompetent OR one that you dated and dumped in high school with a grudge AND that US Attorney convinces a federal magistrate to issue an arrest warrant AND a federal LE agency in your area decides that they will put together a six person crew (minimum for an "unknown" target) to come out to your house to do a controlled delivery THEN you are really in trouble and should immediately run out your front door with your hands up.

Even LE feels a little paranoid when we do something that is in a gray area, trust me. USPS losses packages all the time and mail is stolen more frequently. USPS employees have learned that medicine, cash, and other goodies are mailed and they can/do steal this stuff figuring that no one will complain because of the gray area contents. I have also had beaten up, muddy, ugly packages show up a month late.

Good luck