The drugs bust is one of the kingdom's largest in years and reflects soaring production of amphetamine-type stimulants in Myanmar, which is emerging from decades of military rule.
Six people were arrested in two related seizures of the pills, known as yaba -- "crazy medicine" -- found at a house in Nonthaburi near Bangkok and in a truck in the central province of Phetchabun, authorities said.
"We seized around 5.3 million yaba pills worth around one billion baht," Police Lieutenant General Surapol Thuanthong of the Narcotics Suppression Bureau told AFP by telephone.
"Now production is increasing because it makes a lot of profits", Surapol said. "Minority groups have small factories to make them."
Also Read
It is estimated that at least 1.4 billion yaba tablets -- with an estimated street value of USD 8.5 billion -- are being produced each year in the Golden Triangle region, according to the United Nations Office on Drugs and Crime.
There are an estimated 600,000 yaba users in Thailand.
The drug is mostly made in isolated mobile laboratories hidden in the forests of Shan state in Myanmar, which is also still the second-largest global source of opium after Afghanistan.