Recreational cannabis is now legally available on the high street in California, after the prohibition was lifted on Monday.
Adults aged over 21 may possess up to an ounce of the dangerous drug, and are even permitted to grow plants at home.
Critics point out that legalisation leads to an increase in young people using cannabis illegally, and studies have shown regular cannabis use can lead to serious mental health problems.
Responding to the change, police officials complained that they are already struggling to deal with the cannabis industry. They fear legalisation will increase crime rates.
Sheriff Jon Lopey, of Siskiyou County, said: “We are overwhelmed”.
And Sheriff Tom Allman told Mendocino County officials: “Please do not continue to say that marijuana is a totally harmless herb”.
In Los Angeles County, Sheriff Jim McDonnell said legalisation would be “eye-opening for a lot of people”.
He said: “The public’s perception is that weed is innocuous”, but warned that cannabis contains dangerous amounts of the psychoactive chemical THC.
“Please do not continue to say that marijuana is a totally harmless herb”
Although recreational cannabis has now been legalised in eight states, it is still an illegal drug under federal law.
Under President Obama, enforcement of federal law in states where cannabis was legalised was eased. US Attorney General Jeff Sessions has now reversed that policy.
Recently a Colorado newspaper outlined the damage that cannabis has caused in the state since it was legalised in 2012.
The Colorado Springs Gazette editorial said: “Five years later, we remain an embarrassing cautionary tale.”
The Gazette said the anniversary is “an odious occasion for those who want safer streets, healthier kids and less suffering associated with substance abuse”.
It went on to explain that in the five years since legalisation Colorado has seen a homelessness growth rate which is “among the highest rates in the country”.
“Directors of homeless shelters, and people who live on the streets, tell us homeless substance abusers migrate here for easy access to pot”, the newspaper said.
According to the US National Survey on Drug Use and Health, Colorado ranks first in the US for cannabis use amongst teenagers. Research by the Denver Post also suggests that the number of drivers involved in fatal crashes who tested positive for cannabis has doubled in the past five years.