KOLOKOL-1 (russian Колокол, eng. bell) is an opiate-derived incapacitating agent. Although the exact nature of the active chemical has not been revealed, in all likelihood it is a derivative of the drug fentanyl, possibly the extraordinarily potent carfentanil. It takes effect very quickly, within one to three seconds, reportedly rendering its victims unconscious for two to six hours. Little else is known about this agent.
According to Lev Fyodorov, a former Soviet chemical weapons scientist who now heads the independent Council for Chemical Security in Moscow, the gaseous agent was originally developed around a secret military research facility in Leningrad during the 1970s. Methods of dispersing it were later developed and tested by releasing harmless bacteria through subway system ventilation shafts first in Moscow and then in Novosibirsk. Fyodorov also claimed that leaders of the failed August 201991 Communist coup considered using the agent in the Russian parliament building. 
Use in the Moscow theatre siege
In 2002, Chechen terrorists took a large number of hostages in the Moscow theatre siege, and threatened to blow up the entire theatre if any attempt was made to break the siege. By the third day of the crisis, the Chechens demanded that Russian president Vladimir Putin begin withdrawing Russian troops from Chechnya, or they would begin killing hostages.
Writing in the Moscow daily Komsomolskaya Pravda, Viktor Baranets, a former Russian Defense Ministry official, stated that the Ministry of the Interior knew that any normal riot control agent, such as pepper spray or tear gas, would allow the terrorists time to harm the hostages. They decided to use the strongest agent available. The paper identified the material as a KGB-developed "psycho-chemical gas" known as "Kolokol-1", and reported that "the gas had such an influence on [Chechen siege leader Movsar] Barayev that he couldn't get up from [his] desk". 
Immediately after the siege, Western media speculated widely as to the identity of the substance that was used to end the siege, and chemicals such as the tranquilizer diazepam (Valium), the anticholinergic BZ, the oripavine etorphine, and the anaesthetic halothane were proposed. Two days after the incident the Russian Health Minister Yuriy Shevchenko told a news conference that the gas was "based on a derivative of fentanyl". 
Although the exact nature of the active chemical has not been verified, the Russian language newspaper Gazeta claimed that the chemical used had been trimethylfentanyl, which is an opioid, attributing this information to "experts from the Moscow State University chemistry department". The name may be a mistranslation of "3-methylfentanyl", a superpotent fentanyl analog that is about 1000-times more potent than morphine, that was manufactured and used in the former USSR.
If Kolokol-1 was the incapacitating agent used in the Moscow theatre siege, it appears that it was directly or indirectly responsible for the deaths of over 100 of the 800 hostages, who appear to have died through a combination of the effects of high doses of the incapacitating substance, lack of food and water, and the lack of adequate medical treatment following the raid, which was exacerbated by the refusal of the authorities to reveal to doctors the nature of the incapacitating agent.
If the incapacitating agent in the siege was in fact a fentanyl derivative, and hospitals had been informed of this, intravenous administration of naloxone would have immediately reversed the effect in comatose patients. This drug, normally used to treat opiate overdose, is a pure opiate antagonist. When administered to a patient with uncomplicated opiate overdose, successful recovery is likely. However, since the drug is normally used only for drug overdoses, the hospitals involved may not have had enough in stock to treat everyone, or even the majority of those affected by the agent.
- Goldiner, Dane. Weir, Fred. (October 29, 2002) Gas looks like secret KGB tool New York Daily News
- Peterson, Scott. (October 29, 2002). "Gas enters counterterror arsenal". The Christian Science Monitor, WORLD; p. 1.
- "News Chronology (August through October 2002)". THE CBW CONVENTIONS BULLETIN (Issue 58). 2002. pp. 27–46.