Authorities said on Tuesday that just over one gramme of ketamine had been found in a seizure that police had initially believed contained over 12 tonnes of the drug worth almost US$1 billion (30 billion baht).
Wichai Chaimongkol, secretary-general of the Office of the Narcotics Control Board (ONCB), told a news conference 12.1 tonnes of the haul contained trisodium phosphate -- a chemical which can be used as a food additive and cleaning agent.
The remaining 301 kilogrammes was calcium carbonate and contained just 1.2 grammes of ketamine, he said, adding the seizure was made as part of an international investigation following arrests in Taiwan.
Last month, police announced what they thought was Thailand's largest ketamine drug bust and said it pointed to a multinational drug network.
Authorities later said tests had shown no evidence of drugs and that trisodium phosphate reacted in the same way as ketamine by turning purple in tests.
In medicine, ketamine is used as an anaesthetic or an anti-depressant, but as a recreational drug it is used to induce dreamy or trance-like sensations, and sometimes hallucinations.
The ONCB said the substances came from a warehouse in Chachoengsao. Mr Wichai said the substances were hidden in the warehouse in Bang Pakong district on Saturday.
Mr Wichai said the investigation that led to the discovery of the substances was jointly conducted by the ONCB, the Royal Police Office's Narcotics Suppression Bureau and the Department of Medical Sciences.
The trisodium phosphate was found to be placed in three areas of the warehouse and the remaining substances in another spot on the premises.
Last month, the ONCB had been notified about a major ketamine crackdown in Taiwan believed to have been related to the substance that was found in the Chachoengsao warehouse.
It had also successfully traced the source of the seized ketamine before connecting the raided warehouse with the ketamine seized in Taiwan, according to the Justice Ministry. The United Nations Office on Drugs and Crime alerted the ministry to a similar scenario.