BANGKOK - Large posters of marijuana - until recently illegal in Thailand - have taken over prominent Bangkok street corners in the lead-up to elections on March 24.

A 90-day amnesty is in effect for people who possess the drug in the country, which became the first in South-east Asia to legalise medical marijuana last December.

The Government Pharmaceutical Organisation, a state enterprise, launched the kingdom's first legal marijuana plantation in February in a secure greenhouse, in a cautious bid to grow its own supply for research and medicine.

But the Bhumjaithai political party wants to go further, by turning marijuana into Thailand's next cash crop. It pledges to change the law to allow each household to grow six marijuana plants each - a venture which it says will earn them US$13,000 (S$17,600) per year.

Marijuana is the dried flowers and leaves of the cannabis sativa plant. It contains a mind-altering compound called tetrahydrocannabinol, as well as another substance called cannabidiol, which is not intoxicating.

The drug is outlawed in many countries but legally cultivated in others for cannabidiol, which some studies say can be used to treat ailments such as epilepsy and insomnia.

Bhumjaithai, which grew out of the country's hardscrabble north-east region, won 34 out of 500 Parliament seats in the last election in 2011, putting it in a distant third place after the giant Pheu Thai and Democrat parties.

Analysts expect Bhumjaithai to join any ruling coalition that arises after the forthcoming election. But party leader Anutin Charnvirakul has said that acceptance of its marijuana policy is a non-negotiable condition for it to join any coalition.

"If they don't accept this policy, which is one of our lead policies, how can we join?" he told The Straits Times.

For weeks now, the party has been airing a slew of policy proposals targeted not just at farmers grappling with low commodity prices but also middle-class voters feeling left behind by technological changes.

Bhumjaithai pledges to offer free online learning courses for all and give farmers a bigger share of the final value of their crops like rubber and tapioca, relative to what the distributors typically get. It also wants to legalise the use of private vehicles for ferrying passengers under the Grab ride-hailing platform, to give people more sources of income.

But it is the marijuana proposal that has captured the most attention in a society conditioned for decades to view the plant as a dangerous narcotic alongside heroin and methamphetamines.

"We have seen little opposition from the public," Mr Anutin, a former deputy health minister, said. "Rather, people want to find out how we can expedite it."

Through this policy, the party is advocating for a greater role for small-scale local producers who might otherwise be muscled out of the fledgling medical marijuana industry by patent-wielding international drug conglomerates, he said.

Dr Tares Krassanairawiwong, the secretary-general of the Food and Drug Administration, which plays a key role in controlling access to marijuana, would not comment on Bhumjaithai's proposal.

"This system is not open, but it is loosening," he told The Straits Times. For a trial period of five years, only government-linked entities are allowed to plant marijuana. Even then, the buyers of the final product must be declared upfront.

"We don't want the product to leak," he said. "If it is grown freely, we don't know where the plant will go."

Dr Tares said patients using marijuana on the quiet in the past would in the future have to rely on the new system after registering with the government during this amnesty period.

Under the new system, marijuana-based medicine can be dispensed only with prescriptions from licensed doctors and traditional Thai physicians.

"Marijuana cannot be used for every disease. Patients have to learn and consult with their physicians," said Dr Tares.

Thailand, he said, was only starting to learn about medical marijuana.

"We have to work together to create a system for making the best use of marijuana while limiting its negative effects," he said.