There was a time when you could walk into any corner store and purchase "Mini Thins" which were pure ephedrine HCL, or buy a cold med of a previous generation that had very little or no additional crap added to it. Currently, all the cold medicines made for sale in the US that contain ephedrine or pseduoephedrine contain acrylic polymers which are not actually made by the drug company rather a third party company such as Evonik who is know for their product Eudragit. Eudragit will not be listed on your cold medicine label even thought it, or something similar is in there. While these delivery systems have a number of purposes, one of the "secret" functions is to block the reduction into methamphetamine. They do this by binding to it and preventing the isolation/extraction of the pure ephed. Extracting the pure ephed is a precursor step to meth synthesis. That's why finding the pure stuff is a bit rare. The DEA does not want you to have it. This is all about our meth laws. So you really do have to be careful cause they have a hard-on for anyone that breaks the rules. Also keep in mind if you are in possession of pure ephedrine, and also happen to a have a few other things in the garage or in your medicine cabinet such as iodine, any acid containing hydrochloric acid such as the driveway cleaner muriatic acid and/or red tipped matches, you can be put in jail for a VERY long time. You will not be on their radar, but if you order these pure products, especially in large quantities you will be. So make sure you don't have any of these other products in your home if you are ordering the pure stuff and having it delivered directly to your house.
