The Jordanian army said that members of its border guard on Sunday foiled an attempt to smuggle 900,000 Captagon tablets from Syria.
The troops seized the pills after "a group of people coming from the Syrian territory tried to cross the border illegally".
Captagon is a highly addictive, cheaply produced alternative to amphetamines and methamphetamines. It has become in recent years the most in-demand drug in the Middle East.
Arab security officials say the main centres of production are regime areas of Syria, where hundreds of millions of pills are produced each year by cartels linked to the Syrian regime and pro-Iranian militias supervised by Hezbollah.
A large proportion is smuggled through Jordan to the Gulf. Since last year Jordanian authorities have regularly announced drug busts on the border with Syria, often involving gunfights with smugglers.
Iran and Hezbollah deny any involvement.
Jordanian authorities said last month that Syrian army units and militias supported by Iran are behind a sharp rise in attempts to smuggle Captagon and other drugs over the border.
It was the first time that Jordan publicly implicated the Syrian regime and Tehran in the growing regional narcotics trade, estimated to be worth billions of dollars a year.
Jordan has sought in the past two years to normalise ties with the government of President Bashar Al Assad in Damascus.
Those relations had cooled since the uprising against five decades of Assad family rule in March 2011.
Senior Jordanian army officers met Syrian military commanders in Amman at the end of last year to try to secure Damascus's co-operation in curbing the illicit trade.