I am sorry, but without any imprints, there is no way any of us can tell you for sure what they are. All prescription drugs sold legally in the US are required to have unique individual markings, per the FDA for identification purposes.
These could be anything, something OTC, something from another country, illegal drugs or whatever. Short of paying to have the remaining powder lab tested, there is no way to know for sure.
verwon@gmail.com
My information is not guaranteed correct. I do not get them right all the time, but I do enjoy the hunt~