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.
The Lebanese authorities have foiled an attempt to smuggle a huge quantity of drugs to Saudi Arabia, officials say.