Usnic Acid

Usnic acid is part of a group of compounds known as uncouplers(DNP is anotheruncoupler). Uncouplers are mostly non-polar weak acids that are able to disrupt ATP synthesis. In a nutshell, one of the drivers to produce ATP in the electron transport chain is the energy generated from the H+ gradient(all of the H+ are on 1 side of the membrane which creates an electric potential). Usnic acid can bind with and transport H+ across the membrane, which effectively creates "leaks" in this gradient and it loses energy. Your body still needs ATP, so it draws energy from stored fat to makeup for the loss caused by usnic acid.

 
Reports of losing 5lbs + a week were not uncommon with users of usnic acid. Unfortunately, when you disrupt ATP synthesis, you generate tons of free radicals, which are harmful to your cells. Usnic acid was pulled from the market due to users experiencing acute liver failure. This may have been avoided/lessened if strong antioxidants were taken concurrently. I personally used a product called Lipokinetix years ago that had usnic acid and loved it. While not as strong as DNP, it was a very powerful fatburner and there hasn't been anything even close to the effectiveness brought to market since.