Captagon is the brand name of the drug fenetylline. It is similar to the stimulant drug amphetamine (also known as speed). Fenetylline was once used as a medication for ADHD. It is no longer used medically and is illegal in most countries.
Captagon is mainly used in the Middle East. It is rarely used in the Netherlands. Since it is produced illegally, the pills sold as Captagon may contain other substances.