According to scientists who performed a new set of experiments on unsuspecting mice, it may be that the large number of police jail deaths that took place about a decade ago were caused by the use of pepper sprays on people intoxicated with psychoactive drugs. The investigation raises new questions on the use of the paralyzing spray, which is currently widely employed by police departments and other security forces in cities around the world. The method is preferred because it incapacitates subjects, while not being lethal, NewScientist reports.

In spite of these advantages, just like Tasers, they have come under increased criticism over the years, when policemen using them have inadvertently caused the deaths of several suspects, while in pursuit. The new study is just another piece of evidence to add to those stacked up against using pepper sprays. The investigators, at the San Francisco-based St Luke's Hospital Addiction and Pharmacology Research Laboratory, say that the active element in the sprays, capsaicin, may be interacting violently with psychoactive drugs, which may lead to the suspects' untimely death.

In the early 1990s, many people reported other individuals being attacked with pepper sprays by the police and dying shortly afterwards. When analyzed after their death, those who had died showed signs that they had been taking cocaine, or other psychoactive drugs. John Mendelson, the leader of the new investigation, says that he was surprised and made curious by these anecdotes, and decided to test their truth value on rodents. Several groups of 30 mice each were used for the investigation.

Some of the rodents were injected with capsaicin, cocaine, or both at the same time, in varied doses. This approach allowed the scientists to control the amount of the stuff that the mice were exposed to, something that wouldn't have happened if the animals were simply sprayed. In one group, which received the largest dose of cocaine, a few of the creatures died immediately afterwards. When the same amount of the drug, plus the pepper spray chemical were injected, more than half of them died.

“The presence of capsaicin in mice makes smaller amounts of cocaine more lethal. We don't actually know how capsaicin reacts with cocaine to produce a lethal effect,” the expert says. An even higher dose of cocaine killed half of the mice but, combined with capsaicin, it killed more than 90 percent of the animals. Details of the study appear in the latest issue of the journal Forensic Toxicology.