Kolokol-1

Kolokol-1 (Russian: Колокол meaning "bell") is a synthetic opioid developed for use as an aerosolizable incapacitating agent. The exact chemical structure has not yet been revealed by the Russian government. It was originally thought by some sources to be a derivative of the potent opioid fentanyl, most probably 3-methylfentanyl dissolved in an Inhalational anaesthetic as an organic solvent.

However, the only independent analysis of residues on the Barricade Theater hostage crisis hostages' clothing or in one hostage's urine performed by a team of toxicologists at the United Kingdom's center for research on chemical and biological warfare in Porton Down, Wiltshire, England found no indication that fentanyl or 3-methyl fentanyl were used. Instead, two much more potent and shorter-acting agents, carfentanil and remifentanil, were found in the samples taken from hostages' clothing and urine. They concluded the agent used in the Barricade Theater hostage rescue consisted of highly potent, very short-acting carfentanil and longer-acting but less-potent remifentanil, both fentanyl derivatives which are much stronger than fentanyl itself, in an aerosol suspension.