GETTY Captagon allows those fighting in Syria to stay in battle for hours, often with no food or sleep

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There is some evidence the killers who struck in Paris last Friday may have been high on the drug, which is produced by ISIS chemists and sells across Syria and the Middle East for as little as 90p a tablet. Captagon, the trade name of a now banned German drug designed to treat ADHD, has in it’s copy-cat home-made form, for years been the narcotic of choice for many in the Middle East. The drug, whose generic name is Fenethylline, increases aggression at higher doses and abusers can have aural and visual hallucinations, psychotic episodes or extreme dysphoria that manifests as paranoia or depression. It also carries the risk of heart failure or brain haemorrhages, followed by death.

Long before the start of the conflict, Syria was a major stop-gap for drugs destined to the wealthy markets of Western Europe and the Gulf States. But with the start of the war in 2011 and the breakdown of law and order and basic infrastructure, the drug trade has flourished. Captagon was first produced in the 1960s to treat conditions such as hyperactivity, narcolepsy and depression, but was banned by most countries in the 1980s for being too addictive. The underground trade continued to prosper over the years, however, and today ISIS fighters are using the drug to help them stay alert and on their feet for days, during long, protracted battles.

GETTY At high doses the drug increases aggression, causing visual hallucinations and psychotic episodes

Lebanese psychiatrist, Ramzi Haddad, said Captagon works as a "stimulant" that "gives you euphoria." He said: "You're talkative, you don't sleep, you don't eat, you're energetic." The drug is also thought to have become a major source of income for all those involved in the Syrian conflict. The ingredients and production methods are cheap, yet a Captagon tablet sells for $20 in the black market. ISIS fighters and anti-Assad rebels alike use the proceeds to buy weapons.

GETTY Captagon consumption among civilians is on the rise as they try to cope with the brutal conflict

But it's just not ISIS and anti-Assad rebel fighters who have become hooked to Captagon. Consumption among civilians is also said to be on the rise, as they try to cope with a bloody conflict which has so far killed 200,000 people and caused millions to flee their homes.