The Centre of Addiction Studies has found the number of people aged under 20 who use cannabis recreationally has doubled since the plant was formally decriminalised this year.
The increase has caused concern among critics of the policy over the plant's impact on the physical and psychological health of young people, especially as the effort to pass the cannabis and hemp control bill is currently going nowhere.
CADS director, Ratsamon Kalayasiri, said the increase in recreational cannabis use among Thai youth underlines the need to closely monitor the impact of the policy. Such data could be used to inform lawmakers deliberating the cannabis control bill.
"The use of cannabis for purposes other than medical or research is a sensitive issue, and as such a good system needs to be in place to control access to the plant," Dr Ratsamon said.
Muhammad Fahmee Talib, a lecturer with Prince of Songkla University's Faculty of Medicine, said while the negative impacts of cannabis use are still manageable, there has been a marked increase in the number of patients seeking treatment after consuming cannabis.
Patients seeking treatment for psychological side-effects following cannabis consumption account for about 3% of all ER admissions nationwide last year, but this year, the figure is closer to 17%, Dr Muhammad said.
"The Bhumjaithai Party promoted cannabis as a cash crop prior to its legalisation, and now cannabis is seen as a tourist draw. Thais have to be aware of the negative impact [of this policy]," he said.
Separately, Patcharin Khankham, a senior policy planning analyst at the Office of the Narcotics Control Board (ONCB), said there are growing concerns that locally-grown cannabis which does not meet the standards for further processing into medicinal products might be diverted to the black market to meet demand by recreational users.
She said that up to 95% of domestically cultivated cannabis fails to meet the standards required for further processing.
Meanwhile, a child and adolescent psychiatrist at Siriraj Hospital, Chariya Phuditchinnaphat, said a legal mechanism is needed to ensure producers of cannabis-infused food and beverages accurately list the concentration of psychoactive ingredients in their products.
This will help protect consumers from abuse.
"Recently, three people were admitted to Siriraj Hospital after ingesting cookies which contained more tetrahydrocannabinol that what is legally allowed under Thai laws," she said.
