For the first time in six years, the amount of opium produced in Afghanistan has decreased, according to a new joint survey released Wednesday by the U.N. and Afghan government.

The United Nations Office on Drugs and Crime (UNODC) said Afghan opium cultivation dropped by 19 percent in 2015 compared to the previous year.

The drop was mainly attributed to unfavorable climate conditions, reports The Associated Press. The report authors said the decrease was also due to better cooperation between enforcement agencies and Afghan policy makers, as well as a change in methodology used to estimate areas of poppy cultivation.

Lower levels of cultivation translates to a 48 percent reduction in the potential production of opium in 2015 – 3,300 tons compared to 6,400 tons in 2014, according to The Associated Press.

The average opium yield per acre also dropped 36 percent, and eradication was up 40 percent to 9,290 acres, from 6,650 acres last year.

The Helmand province is still the largest poppy producer, but saw a 16 percent drop since last year, the report said.

UNODC regional representative Andrey Avetisyan said that despite the decline in cultivation, it increased in northern Afghanistan due to the deterioration of security in some places. He emphasized that Afghanistan still has a significant drug problem and needs the assistance of the international community to tackle the issue, but said that cannot be accomplished until the country is stabilized, according to Voice of America.

Afghanistan was the main source of the world's heroin supply for most of the 1990s, but in late 2000, the Taliban enforced a ban on poppy farming, which led to a 99 percent reduction in poppy farming in Taliban-controlled areas, according to Science Direct. But in 2001, the Taliban told farmers they were free to start planting poppy seeds again since the U.S. began military attacks.

Since then, the U.S. has spent $7.6 billion on counter-narcotics efforts in the country, which have largely been ineffective, with opium production increasing 36 percent between 2012 and 2014 alone, according to the Guardian.