It is a record for the country, according to Saudi Arabian authorities, to have recovered 46 million amphetamine pills hidden inside a consignment of flour.
The shipment was followed by security personnel as it entered the Riyadh Dry Port and was transported to a storage facility, according to the General Directorate of Narcotics Control.
Six Syrians and two Pakistanis were arrested in a raid on the warehouse.
The GDNC did not name the amphetamine, but Saudi Arabia is the largest market for tablets bearing the captagon logo.
Captagon – typically a mix of amphetamine, caffeine, and various fillers – is reportedly one of the most popular drugs among affluent youths in the Gulf.
A 2021 Foreign Policy article cited researchers as saying that “boredom and social restrictions”, as well as easy availability, were driving the use of captagon in Saudi Arabia.
The drug has also been consumed by combatants in the civil war in Syria, who say it dims fear on the battlefield.
The global trade in captagon is growing rapidly and was worth an estimated $5.7bn (£4.9bn) last year, according to a recent New Lines Institute report.