Carbon monoxide poisoning is the common form of poisoning worldwide. Just in the US tens of thousands of people are killed or hospitalised every year by this odourless and colourless gas, which in is boiler, stove and vehicle exhausts and is also produced during house fires. At the moment, the only treatment is oxygen, but it's not very effective and often is administered too late. Now researchers at the University of Pittsburgh have developed an antidote molecule that can circulate in the bloodstream and pull the carbon monoxide from tissues to make it safe. Mark Gladwin told Chris Smith how it works, beginning with why carbon monoxide is poisonous in the first place