Recreational use of cocaine, morphine and opium is still illegal, despite easing of some restrictions, Justice Minister Somsak Thepsuthin warned on Wednesday.
They remain as listed category 2 drugs. They have not been removed from the national list of narcotic drugs, the justice minister said.
He issued the warning after the Royal Gazette published a ministerial regulation allowing sale and possession of cocaine, morphine and opium for medicinal and study purposes, and government use.
He said the three substances had not been removed from the list, and the ministry had no policy to remove them.
Mr Somsak said only kratom, a plant containing a natural stimulant, will be removed from the list. It contained only a small amount of the drug. Kratom is currently classified as category 5 on the national drugs list.
Proper consumption of kratom, for example no more than 20 leaves per day, would not have harmful effects on people's health or physical condition, he said.
Once kratom had been officially removed from the list, laws would be issued requiring people to seek official permission to grow it, and to prevent the leaves being sold to children, he said
The Office of the Narcotics Control Board recently passed a resolution to allow growing of kratom in 135 villages or communities. People in these places were allowed to consume and have in it in their possession.
Mr Somsak said the resolution allowed leniency for people to chew the leaves fresh or as a drink after steeping them in boiling water .
Unrestricted use of kratom leaves had not been allowed, he added.
As for marijuana, which is also listed as a category 5 narcotic drug, Mr Somsak said: "We need take marijuana into consideration in two ways - one, as a narcotic plant, and two as a narcotic substance which requires strict control.
Extracts of marijuana should be open to easy access and use for medicinal purposes and research, to provide people with alternatives and hope in fighting against some dangerous diseases."