"Rush" was originally amyl nitrate, a vasodilator that was commonly prescribed to angina patients until people found out that they could enhance their orgasms by inhaling it. Amyl was then made illegal to distribute. It was then substituted with butyl nitrate, isopropyl nitrate, and a host of other nitrate formulas all doing the swame thing, but not as strong as the original amyl formulation.
When inhaled by someone under the influence of alcohol, marijuana, and whatever psychedelic you favour, it can take the back of your head off as you come.
One warning though, you don't want to do too much at once (it can mmake you puke) and once you come down, be sure to open a window.
