Marijuana sales for recreational use began in Oregon on Thursday as it joined Washington state and Colorado in allowing the sale of a drug that remains illegal under U.S. federal law.

Oregon residents 21 years and older can buy up to a quarter-ounce (seven grams) of dried pot at roughly 200 existing medical-use marijuana dispensaries as a new law took effect.

Backers hope the law will help curb a flourishing black market, but opponents say it heightens drug use and access by children.

About 40 people lined up outside the medical pot dispensary Shango in a strip mall near Portland International Airport for the chance to buy recreational pot one minute after midnight, when the changes went into effect.

PORTLAND, Ore. (AP) — Discounts on pot, free food for folks with the munchies and live music will usher in a historic day for Oregon and for marijuana advocates across the country Thursday, as recreational sales of the drug that is still illegal under federal law begin in the state.

Oregon is one of four states that have legalized the sale of recreational marijuana. It will start with far more dispensaries than did Colorado or Washington state, where pot shops have been up and running for more than a year. Alaska could begin retail sales next year.

Recreational marijuana has been legal throughout Oregon for a few months now. While residents could use it, purchasing from a store hasn’t been possible.

That’s because retail sales of recreational cannabis have remained illegal. That ends Thursday, when the state will begin allowing recreational sales at medical marijuana dispensaries.

According to the OLCC, the state currently projects $10.7 million in revenue for the 2015-2017 biennium.

Here’s everything you need to know about purchasing pot for recreational use in Oregon.

What is changing Oct. 1?

PORTLAND, Ore. (AP) -- Oregon marijuana shops began selling marijuana Thursday for the first time to recreational users, marking a big day for the budding pot industry.

Some of the more than 250 dispensaries that already offer medical marijuana in Oregon opened their doors soon after midnight — just moments after it became legal to sell to anyone who is at least 21.

At Portland's Shango Premium Cannabis, co-founder Shane McKee said the first sale to an excited customer came about a minute after midnight, with many others waiting.

"It looks like there is about 60-70 in line out front," he said in a telephone interview shortly after midnight. "They all seem extremely eager."

That first buyer, Davia Fleming of Portland, said the sales launch was important.

ONTARIO, Ore. -- You will soon be able to buy marijuana in a store for recreational use in Oregon.

In July, a new law went into effect making the use and possession of certain amounts of marijuana legal.

Starting Oct. 1 that law will also allow medical dispensaries throughout the state to sell the drug as well.

Ontario Mayor Ron Verini says community members were overwhelmingly opposed to the visibility of marijuana which is why they banned medical dispensaries, that means sales for recreational use aren't allowed in this part of the state.

"Right now the community overwhelming, definitely says, 'No we don't want to see it,'" said Verini.

A closeup of a marijuana plant shows the tiny hairs known as trichomes covering the surface of its leaves. Starting Thursday, adults can buy recreational marijuana in Oregon, the third state to permit legal sales.(Photo: Trevor Hughes/USA TODAY)

Oregon residents can buy legal recreational marijuana starting Thursday, joining just two other states with similar systems.

Adults 21 and older in Oregon may buy up to a quarter-ounce of cannabis per day, without needing a doctor’s recommendation.

Oregon is only the third state to legalize pot in the country

Recreational marijuana has been legal throughout Oregon for a few months now. While residents could use it, purchasing from a store hasn’t been possible.

That’s because retail sales of recreational cannabis have remained illegal. That ends Thursday, when the state will begin allowing recreational sales at medical marijuana dispensaries.

According to the OLCC, the state currently projects $10.7 million in revenue for the 2015-2017 biennium.

Here’s everything you need to know about purchasing pot for recreational use in Oregon.

John Rosman/OPB

Oregon Legislature Clears The Way For Recreational Cannabis Users.

Portland, Ore., Sept. 29, 2015 /PRNewswire/ -- Thanks to the Oregon Legislature headed by its recently installed Governor Kate Brown, starting October 1, 2015, cannabis dispensaries will begin selling cannabis products, including select grade flower, into the Oregon adult recreational-use market.

"Like most people in our State, Chalice Farms, LLC supports the Oregon Legislature's decision to allow licensed medical dispensaries to serve adult recreational clients before OLCC licensing begins," said Chalice Farms Founder and President, William E. Simpson III.

The offices of the Oregon Liquor Control Commission must be busy these days: Not only are employees hammering out the rules under which recreational marijuana will be sold, they’re also keeping track of those local governments that are working to ban the pot sales.

That list gets longer by the week. Currently, it includes mid-valley communities such as Sweet Home and Brownsville. It also includes seven of Oregon’s 36 counties. More governments will join the list, possibly including Albany, where the City Council last week made some noise about maybe pursuing a permanent ban on recreational sales.