The survey this year also found that 170,000 adults, or 1.4% of the adult population, took often-addictive opium and heroin, the UN Office on Drugs and Crime (UNODC) said on Thursday.
This was within the range of addiction rates of neighbouring countries, including Iran (2.8%) and Pakistan (0.8%), it said.
"We are concerned about some results from the survey but also pleased that this will now enable us to take more focused action to tackle this problem," Deputy Minister for Counter Narcotics General Khodaidad said in a UN statement.
Afghanistan is the world's top opium producer.
The survey suggested there were 920,000 drug users in Afghanistan, including about 150,000 who took opium, 50,000 heroin and 520,000 hashish.
Women and children
About 180,000 people also consumed non-prescribed pharmaceuticals such as painkillers, it said.
Other drugs used in Afghanistan included preparations made from cannabis and opium, petrol, glues and alcohol.
Afghanistan produces about 8%
of the world's supply of opium
Eighty percent of drug users were men, 13% women and 7% children, the survey found.
"Also alarming is the rate for injecting drug use: approximately 15% of male heroin users are injecting," the statement said.
The highest level of drug use was in Kabul followed by provinces bordering Turkmenistan and Uzbekistan.
"The findings of the survey will be important to target future activities in drug demand reduction, including prevention as well as treatment," said UNODC representative Doris Buddenberg.
Afghanistan produces about 8% of the world's supply of opium, most of which is used to make heroin used in Europe.
The land under opium poppy cultivation has been drastically cut over the past year, for the first time since the 2001 fall of the Taliban government, the UNODC and US government said in reports released on Wednesday.
Land surface for drug crops had been cut by 21% over the past year to 104,000 hectares (256,000 acres), the UNODC said.
The White House Office of National Drug Control Policy put the figure at 107,400 hectares (265,275 acres) but said it was 48% down on 2004.