Five Saudis, reportedly including a prince, were detained at Beirut's airport after two tonnes of pills branded as Captagon were found in cases due to be loaded onto a private jet.
It was the largest drug smuggling operation yet uncovered at the airport.
Captagon pills, which typically contain amphetamine and caffeine, are consumed widely in the Middle East.
The drug has helped fuel the conflict in Syria, generating millions of dollars in revenue for producers inside the country as well as being used by combatants to help them keep fighting.
NNA reported that 40 bags of Captagon pills were found by inspectors from the Gendarmerie in cases due to be put on board a jet bound for Hael, in northern Saudi Arabia.
It did not identify the Saudi citizens who were detained, but sources told the Associated Press and the AFP news agency that they included a Saudi prince.
In April 2014, Lebanese security forces foiled an attempt to smuggle 15 million Captagon pills hidden in shipping containers full of corn from Beirut's seaport, according to AFP.
Captagon, originally the trade name for the synthetic stimulant fenetylline, was first produced in the 1960s to treat hyperactivity, narcolepsy and depression.
However, it was banned in most countries by the 1980s because of it was too addictive.
In 2013, the UN Office on Drugs and Crime (UNODC) said 64% of global seizures of amphetamine took place in the Middle East, and that most of the amphetamine was in the form of Captagon pills.

Perry Cohen and Austin Stephanos, both 14, were last seen on Friday afternoon buying $110 worth of fuel near Jupiter, before setting off on a 19-foot boat.
Their capsized boat was found on Sunday morning more than 180 miles from where they set off two days before.
"I just want him home. I know he's coming home," said Austin's mother Carly Black on NBC's Today programme.
Pamela Cohen, mother of Perry, told NBC that she believes her son and his friend "are doing everything they can to stay afloat".
She said the two boys have worked with boats their whole lives and that it is natural for them to be on the water.
The two mothers said the boys went fishing offshore when the weather turned and "something went amiss".
The US Coast Guard expanded its search on Tuesday morning, searching up to Georgia and down to Cape Canaveral in Florida through the day and night.
A spokesman said they were still optimistic they can be found alive.
They were last seen buying petrol and authorities said they may have been headed toward the Bahamas.
Nick Korniloff says his stepson, Perry, and Austin were were supposed to stay on a nearby river and waterway when they set out to go fishing on Friday, but they ended up in dangerous waters.
Former American football player Joe Namath, Ms Cohen's neighbour, has offered a $100,000 (Â£64,100) reward for information on the missing boys.
Mr Namath said during a press conference "We've got to believe in their wherewithal".
The Lebanese authorities have foiled an attempt to smuggle a huge quantity of drugs to Saudi Arabia, officials say.
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Authorities are continuing to search for two teenagers who went missing while fishing off the Florida coast.