DENVER - Marijuana users celebrated Wednesday as Colorado became the first US state to allow retail cannabis sales, putting it in the vanguard of efforts across the country to legalize the drug.
The western state famous for its ski resorts and breathtaking mountain vistas has issued 348 retail licenses - including for small pot shops - that can sell up to 28 grams of pot to people aged 21 or older.
Washington state on the Pacific Coast will follow Colorado several months from now, when it also allows stores to begin selling cannabis.
Iraq war veteran Sean Azzariti was the first person to legally purchase cannabis for recreational use in the United States.
"It's an absolute honour, I couldn't be happier. It's a huge stepping stone for other states as well, so it's a huge honour, to say the least," Azzariti told reporters.
Azzariti, who has campaigned to legalize weed, said marijuana helps alleviate his post-traumatic stress disorder symptoms.
As America's attitudes on marijuana use evolve, Colorado and Washington legalized recreational consumption of the drug in November 2012 referendums, but the new rules coming into force allow cannabis shops.
"It just makes it an item of commerce, like going into a liquor store," a gray-haired Charles Pierce, 61, told AFP at the Denver Kush Club, where pot fans lined up in the wind and sleet for the 8:00 am (1500 GMT) opening.
State officials here anticipate that marijuana sales will generate some $67 million in annual tax revenue.
Opponents of legalized cannabis warn that it can lead to higher rates of marijuana use and addiction, even among young people who technically are not sanctioned to use the drug.
They also say that marijuana users face a raft of health and psychiatric problems, noting that pot is often a gateway drug that can lead to abuse of more serious substances.
Supporters hailed its legalization - and legal sale - in Colorado as historic, and a possible sign of things to come elsewhere.
"The state is demonstrating to the rest of the nation and the entire world that regulating marijuana works," said Rob Kampia, executive director of the Marijuana Policy Project, one of the leading backers of the ballot initiative to legalize marijuana.
"It's only a matter of time before lawmakers and voters in more states adopt similar laws regulating marijuana like alcohol."
Colorado's branch of the National Organisation for the Reform of Marijuana Laws told AFP that everyone will benefit.
"It will mean jobs, tax revenue for the state and local jurisdictions, increased tourism and a developing progressive new industry in Colorado," NORML attorney Rachel Gillette said.
Michael Elliott, head of the Medical Marijuana Industry Group, noted that Colorado has licensed medical marijuana businesses since 2010, but said the influx of tourists for recreational use of pot could lead to shortages.
"It's tough to know whether supply will meet demand, mainly because it's tough to know the impact of tourism on this new market," he said.
Tax collectors are eyeing the revenue the newly legalized trade will generate, while cannabis growers and others are also rubbing their hands in anticipation.
Enterprising companies are even offering marijuana tours to cash in on tourists expected to be attracted to a Netherlands-style pot culture - including in Colorado's famous ski resorts.
"Just the novelty alone is bringing people from everywhere," said Adam Raleigh of cannabis supplier Telluride Bud Co.
Medical marijuana is already legal and regulated in 19 US states, and has been allowed in some cases for the past 20 years. And in most of them, private consumption of cannabis is not classified as a crime.
Colorado and Washington are creating a recreational market in which local authorities will oversee growing, distribution and marketing - all of it legal - for people to get high just for the fun of it.
The market is huge: from $1.4 billion in medical marijuana in 2013, it will grow by 64 per cent to $2.34 billion in 2014 with recreational pot added in Colorado and Washington, according to ArcView Market Research, which tracks and publishes data on the cannabis industry.
Washington state is expected to open more than 300 pot shops in June.