I got to watch my step dad die 6 years ago from toxic shedding

My step dad was in his 60s when he died of toxic shedding from a weight loss medication. In February of 2016 he was rushed to the hospital and I got to watch him die. His skin started to shed off like a snake, his skin liquified off his hands and feet. His face fell apart and he started to bleed out his mouth. His skin was liquifying off his body and he was dying of internal bleeding. This took place over the course of two weeks. He started to lose his skin liquifying off his hands and feet, and then it was like he was shedding off like a snake. I'm always in search of the medication that he was on that did this, it was a weight loss pill but I sadly lost the toxicology report and have no idea what the medication was. I'm 14 now so I was only 8 when I saw my dad die. I want to know what toxic shedding is and what substance caused it. I think that it might have been xanax but I'm not sure.