The government has rejected calls for marijuana to be decriminalised so that it can be used freely as a recreational drug, saying Thailand at this point has to focus on its use for medical purposes.

"This is not the time to allow people to smoke pot and laugh all day. We are still struggling to deal with drug problems," Prime Minister Prayut Chan-o-cha said Wednesday.

Drug suppression is the government's priority, he said.

Public Health Minister Piyasakol Sakolsatayadorn, said that while the National Legislative Assembly (NLA) deliberates passing amendments to the 1979 Narcotics Act, the ministry is considering adopting a measure to immediately allow the use of marijuana for medical research.

The ministry now plans to reclassify marijuana as a Type 2 narcotic instead of Type 5 so that marijuana extracts can be used for medical purposes, said Tares Krassanairawiwong, secretary-general of the Food and Drug Administration (FDA).

When reassigned as a Type 2 narcotic, marijuana will be used for four main treatment areas, said Dr Sopon Mekthon, an adviser to the public health minister.

In the first, marijuana extract will be used to treat nausea in cancer patients suffering side effects of chemotherapy, drug-resistant epilepsy in child patients, multiple sclerosis and severe pains, he said.

In the second, the ministry plans to use marijuana in Thai traditional medicine, he said.

Thirdly, the Department of Medical Science will study the possibility of using marijuana on patients with Parkinson's disease, Alzheimer's and dementia, he said.

Lastly, the ministry plans to carry out laboratory studies to see how effective marijuana is in treating other diseases including cancer, he said.

This is a first step toward totally legalising marijuana use for medical purposes, so not everyone will be allowed to grow the plant freely, he said.

The handling of marijuana will be strictly controlled at all stages from growing the plant to using it for medical purposes, he said.