Up to 1.3 million speed pills were seized from four Chiang Mai residents suspected of being members of a drug trafficking gang.
The NSB believes the gang smuggles drugs into Thailand over the border with Myanmar near Chiang Mai's Chiang Dao district.
The suspects are Achin Khamphoem, 21, Seri Serirat, 34, Phon Serirat, 35, and Songphop Sae-Chin, 36.
The drugs were found hidden in pickup trucks, covered with bags of corn seeds.
Another lot of 730,000 speed pills and 30kg of crystal methamphetamine were seized from suspects in Chiang Rai.
Police investigators believe the drugs were to be transported via the Thai-Myanmar border to Mae Sai district in Chiang Rai province.
The suspects fled after a shootout with the officers. No one was hurt.
The NSB said Sa Sae-Tho, a Chiang Rai resident, was among the suspects.
In Bangkok, NSB officers arrested Nikhom Sainon, 43, and Sommai Khunsetkuea, 39, in Bung Kum district.
About 794,000 speed pills were found hidden in three suitcases.
A fourth gang allegedly had 10,000 speed pills and 27kg of crystal methamphetamine in their possession.
Five suspects were arrested in Nakhon Pathom's Sam Phran district and Samut Sakhon's Muang district.
The suspects are Sonsak Chuicharoen, 33, Songphon Puklam, 19, Wanchai Suanchan, 23, Charoensuk Sophonwimonkit, 30 and Sawarak Soiampha, 23.
In Bangkok, NSB police apprehended Guinean national Barry Aguibou, 34, at a hotel in Ratchathewi district for possessing 1kg of crystal methamphetamine.