The huge cache of drugs was discovered when a couple attempted to drive their six-wheel truck loaded with bags of recyclable waste through a road checkpoint at the intersection in Kanchanaburi’s Thong Pha Phum district at 3.30pm.
The checkpoint was manned by personnel from the Suranaree Taskforce, Thong Pha Phum police station and district officials.
Officials noticed that the driver, identified only as Pitiphan, 30, appeared intoxicated.
He was asked to take a roadside urine test, which registered positive for drug use.
Pitipan and his wife, Pornsiri, 24, were arrested while their truck was impounded at Thong Pha Phum police station for further checks.
More meth pills were found during the search at the police station.
The officials estimated that about 50 million pills were hidden among the garbage.
The seizure ranked second in terms of Asian meth busts, beaten only by 55 million meth tablets confiscated in Laos near the Golden Triangle, said Jeremy Douglas, Southeast Asia regional representative for the United Nations Office on Drugs and Crime.
Douglas told Reuters that criminal gangs working with ethnic armed militias were flooding Thailand and countries beyond with methamphetamine produced in Myanmar's Shan State.
Narcotics production in Myanmar’s Golden Triangle has risen sharply in the wake of the 2021 coup, which plunged much of the country into chaos and conflict.
Thailand has responded by stepping up border patrols and announcing plans to tighten the drug-possession law so that anyone found with more than one meth pill faces jail as a dealer.