Theeradet Rahothan, 27, was arrested in his white Toyota Vios while parked on the Rangsit-Nakhon Nayok Road in Bueng Nam Rak sub-district of Thanyaburi district on Thursdday night.
Police and ONCB staff had been following the suspect for some time agfter receiving a tip from an informant, said Pol Gen Pongsapat Pongcharoen, secretary-general of the Narcotics Control Board.
After the arrest, police searched the suspect's home in the Phrae Maphon housing estate in the same sub-district and found 40,000 more speed pills.
At the house, authorities also found a Kasikornbank passbook of a woman Mr Theeradet knew. On June 8 alone, it showed 14.47 million baht transferred to the bank account electronically and 14.45 million withdrawn less than an hour later.
Pol Gen Pongsapat said officers suspected the sum was drug money and that some bank staff had illegally facilitated such huge and abrupt transfers.
Methamphetamine or ya ba pills sell on the street for between 200 and 300 baht each but the suspect claimed his margin was only one baht per pill, officers said.
They said Mr Theeradet also told them that he left drugs at certain roadside locations as instructed by an inmate in the Rayong prison but did not see those who picked up the drugs later.