Pol Col Jitkasem Sonkam, the superintendent Tha Rua police station in Ayutthaya, said Padungsak Meeta, 29, was arrested after police found 2,000 speed pills and 37,000 baht in cash in his pickup truck.
Mr Padungsak told investigators that the drugs were to be delivered to a client in Ayutthaya's Pachi district.
After further questioning, police later raided a home of Puangtong Nil-kla, the suspect's wife, and found an unregistered .38 handgun and 50 rounds of ammunition.
The couple confessed that they had been selling meth pills between the adjoining areas of Saraburi and Ayutthaya for a long time.
In Chiang Rai, a 28-year-old woman was caught hiding two bags of crystal meth in her underwear.
Pol Col Weerawuth Chaichanamongkol, the superintendent of Mae Chan police station, said the woman was named Pim Kamwong.
The suspect was on a Bangkok - Mae Sai passenger bus before being arrested.
Ms Pim told police that the crystal meth was given to her by a Myanmar woman in Mae Sai district and she was to be paid 70,000 baht after the drug was delivered to a client in Bangkok.