Captagon has been around in the West since the 1960s, when it was given to people suffering from hyperactivity, narcolepsy and depression, according to the Reuters report. By the 1980s, the drug's addictive power led most countries to ban its use.
The United State classified fenethylline ("commonly known by the trademark name Captagon") as a Schedule I drug under the federal Controlled Substances Act in 1981, according to the National Criminal Justice Reference Service
Still, the drug didn't exactly disappear.
VOA notes that while Westerners have speculated that the drug is being used by Islamic State fighters, the biggest consumer has for years been Saudi Arabia. In 2010, a third of the world's supply — about 6.3 tonnes — ended up in Saudi Arabia, according to Reuters. VOA estimated that as many as 40,000 to 50,000 Saudis go through drug treatment each year.
"My theory is that Captagon still retains the veneer of medical respectability," Justin Thomas, an assistant professor of psychology and psychotherapy at the UAE's Zayed University and author of Psychological Well-Being in the Gulf States, told VOA in 2010. "It may not be viewed as a drug or narcotic because it is not associated with smoking or injecting."