Deputy police chief Pol Gen Somyot Poompanmuang told a press conference on Friday that Somrak Muijaiboon and Veeravat Bamrung were arrested in Rayong with 82,000 speed pills.
Mr Veeravat is a former adviser to the president of the tambon Wang Wa local administrative organisation in Klaeng district of Rayong.
Both suspects said a male inmate known only as "Sua" at the Rayong prison had ordered them to deliver the pills to buyers in three southern border provinces. The suspects were also connected with northern traffickers, the deputy police chief said.
Three inmates at the Rayong prison were later found with mobile phones with logs showing calls placing the drug orders. They were moved to a maximum security prison.
In Suphan Buri, Khanchit Phaensomboon and his wife Pharujee Thiangtham were arrested while receiving 10,600 speed pills from Suphawat Srichaona on Malaiman Road in U Thong district.
Mr Suphawat said an inmate he knew only as "Piak" at Thong Phan Phum prison in Kanchanaburi province had ordered him to deliver the drugs to Mr Khanchit.
In Bangkok, Noppadol Noichoi, 21, was arrested with 30,000 methamphetamine pills on Chalerm Phrakiat Road in Prawet district on Thursday. Police searched at his house there and found 50,000 more speed pills.
The former drug addict said a drug prisoner he knew ony as "Uan" in the Bang Kwang Central Prison of Nonthaburi province had ordered him to pick up packs totalling 100,000 speed pills hidden on Ram Intra Road on June 29. He was then instructed to divide up the drugs and place packets of 2,000 pills each at specified locations.