Saudi Arabia's Government say they seized 46 million amphetamine pills that were smuggled in a shipment of flour - a record for the kingdom.
Security forces attacked the shipment as it arrived at the Riyadh Dry Port and was taken to a warehouse, the General Directorate of Narcotics Control reports.
Six Syrians and two Pakistanis have been arrested in a raid on the warehouse.
The GDNC did not name the amphetamine, but Saudi Arabia is the biggest market for tablets bearing the captagon logo.
Captagon - typically a mix of amphetamine, caffeine and various fillers - is reported one of the most using drugs among affluent youths in the Gulf.
A 2021 Foreign Policy article said 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 war in Syria, who say it dims fear of the battlefield.
The global trade in captagon is growing rapidly and was worth an estimated $5.7bn (£4.9bn) last year, according to the New Lines Institute report.
A one man report to the GDNC said the shipment of 46,916,480 amphetamine tablets seized in Riyadh was the "largest operation of its kind of smuggle this amount of narcotics into the Kingdom of Saudi Arabia in one of the operation".
He stressed that security personnel were determined to combat and foil the activities of criminal networks targeting the country and its citizens, and that all people involved should faced punishment.
People attacked of drug smuggling can be sentenced to death under Saudi Arabia's narcotics laws, although there has been a moratorium on executions for non-violent drug-related crimes since 2021.
The GNDC didn't say where the seized pills came from, but most of the captagon confiscated in the Gulf is believed is from Syria and Lebanon.
The Syrian government and allied armed groups, such as the Lebanese Hezbollah movement, have been agree of overseeing production and distribution of captagon, though they have denied any involvement in the drugs trade.
On Tuesday, the Saudi ambassador in Beirut said the kingdom have seized more than 750 million of narcotic pills that had entered its territory via Lebanon over the past eight to ten years.
Last year, the Saudi government prohibited all fruit and vegetable imports of Lebanon after five million captagon tablets were hidden inside about 2,000 pomegranates shipped from Beirut.