Cannabis advocates are calling on the government to set up a committee to study the impacts of the plant before proceeding to relist it as a narcotic.
Prasitchai Nunual, secretary-general of the Writing Thai Cannabis' Future group, which held a protest near Government House on Monday, said the study should cover physical health, mental health, its effects on society and its therapeutic benefits compared to tobacco and alcohol.
He said if the findings show that the impacts of cannabis are no worse than those of tobacco and alcohol, a special law should be enacted to regulate its use.
If the findings suggest otherwise, the plant should be controlled as a narcotic.
"A committee should study the issue. The facts should be established and laid out for the public to see," he said.
Mr Prasitchai also claimed the change in the cannabis policy is an attempt by certain government figures to protect the interests of major players who stand to benefit from reclassifying cannabis as a narcotic in the name of protecting people's well-being.
Last week, the Public Health Ministry's committee controlling illegal drugs voted to support the reclassification of cannabis and hemp as narcotic drugs except for their branches, leaves, roots and seeds.
Cannabis buds and any materials containing more than 0.2% tetrahydrocannabinol (THC) will once again be criminalised.
On Monday, the protesters also threatened to expose alleged ties between influential financial groups and politicians, particularly those in the ruling Pheu Thai Party leadership.
Meanwhile, a community enterprise in Nakhon Ratchasima's Phimai district is urging the government to assist small-scale cannabis businesses affected by the government's failure to transform it into a new cash crop.
Thongchai Posawang, leader of a community enterprise that grows medical cannabis, said the group has signed a memorandum with the Department of Thai Traditional and Alternative Medicine.
However, growing cannabis for medical use incurs high costs while the price of harvesting is not as good as expected, he said, adding the group has suffered heavy losses and has no hope of recouping investments made.
Now, the group is concerned about whether farmers will still be allowed to grow the plant, he said.
"We'd like to know what measures the government has in store to help the farmers who fell for their campaign words," he said.
"Will the government allow farmers to grow cannabis for medical use and research after this?" he added.
According to Mr Thongchai, the community enterprise was established in 2020, and more than 230 farmers joined.