Police on Wednesday intercepted a pick-up truck at a checkpoint in tambon Salokbat in Kamphaeng Phet's Khanu Woralaksaburi district.
In a subsequent search officers recovered 500,000 methamphetamine pills from the vehicle. A woman and four men who were travelling in the pick-up truck were arrested and charged with possession of drugs with intent to sell.
The action followed a tip-off that the woman, identifed as Kanokwan Sathitpraiwan, and the four men were delivering the pills from the North to drug traders in Nakhon Sawan.
Police on Tuesday arrested Asari Kalatae, 32, of Pattani, and Rusdi Dolo, 27, of Songkhla, with 3kg of crystal methamphetamine and 216,000 methamphetamine pills after their car was intercepted in front of Don Mueang airport.
The police said they were delivering the drugs from a Central province to dealers in the South.