“We handed the British man over to the international affairs department of the office of the attorney-general,” said Jirapop Phuridet, a police lieutenant general within the Central Investigation Bureau.
“He has denied the charges, but we are preparing to deport him back to the UK,” he added.
Authorities added that Mr Ransome had been taken to Bangkok for further legal proceedings. He will be kept in jail until a deportation flight is arranged.
He is not the only British national arrested on drug charges in the Southeast Asian country.
In May, tourist Jamie Louis Swain, 29, was charged with importing and possessing narcotics after an immigration office at Phuket airport found a bag of cocaine while checking his passport.
Charly Garcia, 48, was arrested in March by police in the northern city Chiang Mai and charged with possessing and selling narcotics including cocaine, ketamine and magic mushrooms to tourists.