Highway Police Chief Pongsit Sangphet said the speeding truck of driver Ong-art Chengya was stopped Wednesday morning at a checkpoint, and officers found the drugs under crates of vegetables.
The drugs have an estimated street value of 390 million baht ($11.7 million), the Bangkok Post reported.
Police said the driver attempted to bribe the officers at the checkpoint, first with 200 baht ($6), then with 2,000 ($60), but they refused, adding he later confessed he was hired to drive the pills to a major drug dealer in Phuket, Thailand, province for 20,000 baht ($600).
Deputy Prime Minister Chalerm Yubamrung said the drugs were produced in neighboring Myanmar.
Scarlett Johansson steps out with fiance after pregnancy reveal
Interpol investigating stolen passports on missing flight