legally and sold openly over the Internet, being actively marketed by several Chinese chemical companies. Moscow theater hostage crisis In 2012, a team of researchers at the British chemical and biological defence laboratories at Porton Down found carfentanil and remifentanil in clothing from two British survivors of the 2002 Moscow theater hostage crisis and in the urine from a third survivor. The team concluded that the Russian military had used an aerosol mist of carfentanil and remifentanil to subdue Chechen hostage takers. Researchers had previously surmised from the available evidence that the Moscow emergency services had not been informed of the use of the agent, despite being instructed to bring opioid antagonists to the scene. Unaware that hundreds of patients had been exposed to high doses of strong opioids, the emergency workers failed to bring sufficient quantities of naloxone and naltrexone to counteract the effects of carfentanil and remifentanil. As a result, one hundred twenty-five people exposed to the aerosol are confirmed to have died from respiratory failure during the incident. Potential as a chemical weapon The toxicity of carfentanil in humans and its ready commercial availability has raised concerns over its potential use as a chemical weapon of mass destruction by rogue nations and terrorist groups. The toxicity of carfentanil has been compared to that of nerve gas. Society and culture Legal status China Carfentanil has been controlled in China since 1 March 2017. The trade war between China and the United States has included controversy over the effectiveness of this control. Germany Carfentanil and its stereoisomers and salts are controlled by the Betäubungsmittelgesetz as a anlage I substance and can only be used with the special permission of the authorities United States Carfentanil is classified as Schedule II under the Controlled Substances Act in the United States with a DEA ACSCN of 9743 and a 2016 annual aggregate manufacturing quota of 19 grams (less than 0.7 oz.). United Kingdom Carfentanil has been specifically controlled as a Class A drug since 1986. See also Opioid potency comparison References 1974 introductions Anilides Belgian inventions Carboxylate esters Fentanyl General anesthetics Janssen Pharmaceutica Methyl esters Mu-opioid receptor agonists Piperidines Propionamides Synthetic opioids Veterinary drugs Incapacitating agents