The use of cannabis by young people and admissions for cannabis-abuse treatment have not increased in a US state since it was legalised, according to a new analysis by the state legislature's think-tank.
Under Initiative 502, Washington state's legal-cannabis law, the Washington State Institute for Public Policy is required to conduct periodic cost-benefit analyses of legalisation on issues ranging from drugged-driving to prenatal use of cannabis.
One of those reports was due on Friday (Saturday NZ time) after three years of legal sales. But the report was limited in scope to just a few effects - including the degree of youth use and adult use, treatment admissions and criminal convictions.
"In my overall appraisal, there's not much evidence I-502 has caused changes in the outcomes we looked at," said Adam Darnell, the lead researcher and author of the report.
One exception is that researchers found adults used more cannabis in parts of the state with higher per-capita sales, Darnell said.
The findings represent a "snapshot of our progress to date and are an intermediate step towards the ultimate cost-benefit analysis of I-502", the report states.
"Results may change as implementation of the law progresses and more outcome data become available."
The report arrived shortly after US attorney-general Jeff Sessions criticised the legalisation of cannabis in Washington.
Governor Jay Inslee and state attorney-general Bob Ferguson hit back at Sessions' critique. They said it was based on outdated information and faulty conclusions.
Inslee and Ferguson have said they want to meet with Sessions to help him understand Washington regulations and safeguards.
The institute also has published details about jobs and wages in the legal cannabis industry that were separate from the analysis published on Friday.
At the end of last year, the industry accounted for the equivalent of 6227 full-time jobs, according to the public policy instate, whose mission is to provide nonpartisan practical research.
Wages paid from 2014, when the first businesses were licensed, through to 2016 totalled US$286 million (NZ$400m).
The average hourly wage stood at US$16.45 but that was elevated by a few highly paid workers, researchers said. The median wage was US$13.44. Licensed cannabis businesses averaged nine full-time employees.
The institute's findings on youth use were not surprising as they were based on a biannual survey by the state Department of Health of students in the sixth, eighth, 10th and 12th grades released earlier this year.
Cannabis use by students in all four grade levels was stable or has fallen slightly since I-502 was enacted, the report said.
For example, 17 per cent of the 10,835 second-year high-school students surveyed last year said they used cannabis in the previous month. The level was 18 per cent in 2006 and 20 per cent in 2010.
Legalisation was approved by Washington voters in November 2012. Legal sales began in July 2014.
Adults living in counties with higher levels of legal sales were more likely to use cannabis and do so more frequently, based on state telephone surveys, the report said.
"It's not earth-shattering that people were using more of a product they're buying more of," Darnell said.
While researchers were comfortable reporting that relationship, they did not provide details on those higher levels because they want more data before doing so.
On cannabis abuse, researchers found that admissions for publicly funded treatment fell in the three years after I-502 was enacted. Admissions dropped from 7843 in 2012 to 6142 in 2015.
There is no evidence, the report said, that legalisation caused the decline. Without more data "we don't know if the decline would be greater" if marijuana remained illegal, Darnell said.
In another unsurprising finding, misdemeanour convictions for cannabis possession by adults dropped sharply after legalisation, according to the report.
Prohibitions for minors did not change under I-502; possession remained illegal for them. But convictions began to decline in 2012, dropping from 1015 at the start of the year to 722 in early 2013. The report did not ascertain why.