Thailand on Monday effectively revoked all foreign patent requests for the use of marijuana, after fears foreign firms would dominate a market thrown open last month when the government approved the drug for medical use and research.
The National Legislative Assembly voted to amend the 1979 Narcotic Act in December in what it described as "a New Year's gift to the Thai people".
Until the 1930s, Thais used marijuana to relieve pain and fatigue.
While countries from Colombia to Canada have legalised marijuana for medical or even recreational use, the drug remains illegal and taboo across much of Southeast Asia.
But in Thailand, the main controversy with the legalisation involved patent requests by two foreign firms, British giant GW Pharmaceuticals and Japan's Otsuka Pharmaceutical, filed before the change to the law.
Thai civil society groups and researchers feared domination by foreign firms could make it harder for Thai patients to get access to medicines and for Thai researchers to get marijuana extracts.
Gen Prayut Chan-o-cha issued a special executive order on Monday enabling the Department of Intellectual Property to revoke all pending patents that involve cannabis or remove marijuana from those patents, within 90 days.
"The pending patent requests are illegal," Somchai Sawangkarn, a member of parliament responsible for amending the Narcotic Act told Reuters.
"This NCPO order is beneficial for Thai people across the country because it prevents a monopolistic contract," he said referring to the junta by its official name, the National Council for Peace and Order.
Reuters did not have contact details for spokesmen for either of the two foreign firms and the companies did not immediately respond to emailed requests for comment.
Companies with a request pending can appeal to the Department of Intellectual Property, the government said in an order, published in a Royal Gazette.
Marijuana remains illegal and taboo across much of Southeast Asia, and traffickers can be subject to the death penalty in Singapore, Malaysia, and Indonesia.
The new legislation on marijuana has yet to come into effect. All Thai laws must receive royal approval.