I am taking pregabalin both recreationally and as a proper medication. I live in Poland so it was pretty easy for me, all I had to do was lie on an online psychiatrist form stating that it is a continued medication, but if you live in a country where the regulations are more strict then all you have to do is self-assess the symptoms that are usually medicated for by pregabalin. That is social anxiety, pain, epilepsy, etc. The last one is a bit hard since people usually have a medical history for that, but I have social anxiety that manifests in many different weird situations and pregabalin truly does help me with that. To be frank, if your country allows pregaba to be presribed by a family doctor, then just go to one, say you have social anxiety, you've taken a few pills from a friend and it truly did help you, should do the trick.
Edit: Also, it might be the wrong board to post about things like that, as you've yourself stated that it is not for CTB, especially since pregabalin has no place in a CTB process.