The law was passed unanimously at the Thai National Legislative Assembly by a vote of 166-0 with 13 abstentions.
These changes will legalise the production, import, export, possession and use of cannabis and kratom products for medical purposes.
The change is the first "baby step" to shifting rather archaic laws concerning weed in Southeast Asia, which now sees the death penalty attached to trafficking in some neighboring countries.
Lawmaker Somchai Sawangkarn said the passing of an amendment to allow medical marijuana in the country "could be considered as a New Year gift to Thais".
The junta-appointed parliament in Thailand, a country which until the 1930s had a tradition of using marijuana to relieve pain and fatigue, voted to amend the Narcotic Act of 1979 in an extra parliamentary session handling a rush of bills before the New Year's holidays.
Though many countries have eased up law to use cannabis for medicinal purposes, Canada, Uruguay and South Africa are the only 3 countries where the use of recreational cannabis is legal.
Before this pro-pot political wave, there had been little tolerance for marijuana in Southeast Asia.
Southeast Asia is known for having some of the harshest anti-drug laws in the entire world, and drug dealers can often be subject to the death penalty. The Malaysian Prime Minister, Mahathir Mohamad, said that the sentence should be reviewed.
It added that despite being classified as an illegal drug, many patients have used cannabis to treat their diseases.
The main controversy surrounding marijuana in Thailand involved patent requests by foreign firms that could allow them to dominate the market, making for more hard access for Thai patients and researchers.
Cannabis is legal for recreational use under many USA jurisdictions, and was recently made available on prescription via the U.K. National Health Service.
This military drafted a national Constitution, which calls for Parliamentary elections early next year.
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