This chemical has stuck in my memory since the 1990s, thanks to Uncle Al on sci.chem:
https://en.wikipedia.org/wiki/SF-6847
It is an uncoupling agent [1] with approximately 1800 times the potency of 2,4 dinitrophenol (the compound discussed in the substack post). This means that it is probably deadlier than most nerve gases in humans, milligram for milligram.
The "Uncoupler" wikipedia page I linked is a decent starting point for other chemicals in the class. Many would presumably drive weight loss like 2,4 DNP itself; and most of those would also incur similar side effects ranging from inconvenient to lethal.