A gathering of cannabis advocacy groups outside Government House who are opposed to the relisting of the plant said they will stay there until a law to control its use was enacted.

Led by Prasitthichai Nunual from the People's Network for Cannabis Legislation in Thailand, some 300 pro-cannabis protesters on Sunday began their rally against the blacklisting of the plant.

The plant was decriminalised in 2022 after the Bhumjaithai Party made the issue its flagship campaign policy ahead of the 2019 election.

However, decriminalisation happened before the legislation needed to control and regulate its use and raised concerns about abuse, particularly among younger age groups.

A cannabis and hemp bill passed its first reading but was rejected in the second.

With the Pheu Thai-led government planning to relist cannabis as a narcotic drug, speculation was rife that a law needed to control the plant's use would be unnecessary.

Mr Prasitthichai said the cannabis advocacy groups would stay as long as it took to pressure the enactment of the law to regulate cannabis use.

"It's no worse than tobacco or alcohol and has medicinal properties," he said.