ISIS fighters are using an illegal drug known as Captagon, according to news reports.
But what is the drug and how does it work? Live Science reached out to drug experts for information on the tablet that is rumored to be turning ordinary men into "supersoldiers."
Captagon is actually a combination of two drugs, theophylline and amphetamine, said Nicolas Rasmussen, a professor of history and philosophy of science at the University of New South Wales in Australia.
The combination itself is inactive in the body, but when the body breaks it down into the two component parts, each part becomes active, Rasmussen told Live Science. [Breaking Bad: 6 Strange Meth Facts]
Theophylline is similar to caffeine, but it also opens up a person's airways, and is sometimes used to treat people with asthma. Amphetamine, on the other hand, is the main psychoactive ingredient in Captagon, he said.
"Amphetamines speed everything up," said Richard Rawson, the co-director of UCLA Integrated Substance Abuse Programs. They produce feelings of pleasure and increased alertness, and they reduce the need for sleep and food, he said.
But Captagon — also known by its generic name fenethylline — is actually relatively mild in the world of amphetamines and amphetaminelike drugs, Rawson told Live Science.
Carl Hart, a professor of psychology and psychiatry at Columbia University, agreed.
It's an "inferior amphetamine," Hart told Live Science. In fact, Captagon is milder than Adderall, he said.
Like Adderall, Captagon was once used to treat behavioral problems.
It was used in the 1960s and 1970s to treat people with attention deficit disorder, Rawson said. It didn't seem to have some of the side effects of other stimulants, he said. But it also didn't have many advantages either, and was eventually phased out, he said.
Despite fizzling out in the United States, the drug has been popular in the Middle East for some time.
Abuse of it has "been a problem in Saudi Arabia now for well over a decade," Rawson said.
Just like taking an amphetamine, taking Captagon increases a person's blood pressure, heart rate and alertness, Hart said.
Its other effects are similar to those of just about any type of amphetaminelike substance, Rawson said. People who take it feel more energized, more aggressive and are able to work longer hours, he said. [5 Experts Answer: Can Drug Stimulants Help You Work?]
At low doses, the risk of harmful side effects is low.
"We have people in our society who have been using amphetamines for decades, and at proper doses they're fine," Hart said. It's similar to how we consume caffeine, he said.
But at higher doses, the negative side effects of amphetamine use start to show, he said.
People who take high doses of stimulants may not sleep or eat, which can lead to health problems, Hart said. But these problems are less from the drug itself and more from the effects of skipping sleep or food, he added.
Rawson agreed — people could take a drug like Captagon at low doses for a long time and be fine, he said. They wouldn't experience significant consequences, he said.
But at high doses, the drug can lead to problems such as higher blood pressure, stroke, psychosis and violence, he said.
One purported effect of Captagon is that it makes users feel no pain, but Rawson dismissed this claim.
"We've heard that with stimulants for years," he said. "It's not a magical painkiller."
Instead, the perceived inability to feel pain is a byproduct of a strong stimulant effect, Rawson said. "When you're hyperstimulated and very focused, you tend not to react to pain as much," he said.
As for Captagon turning fighters into supersoldiers, in reality, its effects are "nowhere near what the media reports have been talking about," Hart said. "Trust me, if this drug produced a supersolider, U.S. soldiers would be using it," he said. (The U.S. military has given other stimulants to soldiers since World War II, Hart added.)
Still, there's a chance that people using the drug feel it gives them superior abilities.
It's possible that the fighters taking Captagon truly find the effects to be "spectacular," Rawson said. But he attributed this to a general lack of experience with drugs among the users. If someone with more experience with drugs, or even experience with alcohol, took Captagon, they would likely say that it was much weaker than what its effect would be on someone with little drug experience, he said.
However, as for the use of Captagon by ISIS, it's also possible that what the fighters are actually taking is not Captagon.
"As far as I know, no one's actually [tested] the stuff that's being sold or manufactured," Rawson said. "My suspicion is that it could likely be meth[amphetamine] that's sold under the name Captagon," he added.
Follow Sara G. Miller on Twitter @SaraGMiller. Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.