Anyone who practices medicine although he is not known to have learned medicine is liable (to compensate any damage) [Ibn Maajah]
"«مَنْ تَطَبَّبَ، ولا يُعْلَمُ مِنْهُ طِبٌّ، فهو ضامِنٌ» [حسن.] - [رواه أبوداود والنسائي وابن ماجه.]"