As The Washington Post's Liz Sly recently noted, the war in Syria has become a tangled web of conflict dominated by "al-Qaeda veterans, hardened Iraqi insurgents, Arab jihadist ideologues and Western volunteers."

On the surface, those competing actors are fueled by an overlapping mixture of ideologies and political agendas.

Just below it, experts suspect, they're powered by something else: Captagon.

A tiny, highly addictive pill produced in Syria and now widely available across the Middle East, its illegal sale funnels hundreds of millions of dollars back into the war-torn country's black-market economy each year, likely giving militias access to new arms, fighters and the ability to keep the conflict boiling, according to the Guardian newspaper.

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