Poppy fields now cover a total area of 37,300 hectares, 10 per cent less than the year before, the UN said in a new report titled the Myanmar Opium Survey 2018.
In the report, the UN Office on Drugs and Crime (UNODC) said the reduction amounted to a drop of 520-550 tonnes in production, equivalent to around 53 tonnes of heroin.
Most opium production in Myanmar is concentrated in the northern states of Kachin and Shan.
"Entrenched poverty and opium cultivation in Myanmar are closely connected. Poor opium farming areas need better security and sustainable economic alternatives," UNODC Myanmar Country Manager Troels Vester said in a statement.
"Crime groups are using unstable and insecure parts of the country to do business, and without addressing lawlessness these areas will continue to be a safe haven for those who profit from the drug trade," he added.
The UN agency said that the decline in opium cultivation needed to be understood in the context of the "dramatically changing" regional drug market, which is shifting to synthetic drugs, especially methamphetamine.
The International Crisis Group said in a report this week that Myanmar had become one of the biggest producers of crystal methamphetamine, which is much more lucrative than heroin or amphetamine, drugs that have been produced for decades in the conflict-ridden northern region of the country.