Sean Azzariti, a former Marine who served in the Iraq war and has post-traumatic stress disorder, shakes hands and thanks store owner Toni Savage-Fox, after Azzariti was the first to buy retail marijuana at 3D Cannabis Center, which opened as a legal recreational retail outlet in Denver, on Wednesday Jan. 1, 2014.

(AP Photo/Brennan Linsley)

Five years ago in Denver, Jan. 1 didn't just herald the start of 2014.

That year, New Year's Day also ushered in the world's first fully legal, licensed recreational marijuana stores in Colorado.

More than $1 billion in sales later in Denver alone, dozens of other cities, states and even countries have joined Colorado. One of the leaders of the Centennial State's charge since day one is Ashley Kilroy, Denver's Director of Excise and Licenses.

Kilroy was able to actually get some sleep the night of Dec. 31, 2013, despite the cloud of concern surrounding the day ahead. Would people camp out all night and smoke their newly purchased weed in public? Would the stores run out of supply?

Those fears did not prove to be true, due to the city's strategic awareness campaign, and the fact that citizens took responsibility for their purchases, Kilroy said.

"What we still see is marijuana's an issue that people feel passionately about on either end of the spectrum. Whether it's the reefer madness spectrum or maybe the other spectrum, that this is the best thing since sliced bread," Kilroy said.

One trend Kilroy and her team didn't expect was the popularity of marijuana edibles, with a large number of people wanting to eat, rather than smoke, marijuana. The appeal of edibles to novice marijuana users combined with a lack of consistent labeling and THC dosage became a problem.

"There were no real regulations around it. As soon as we realized that was an issue, we all began working really quickly on this. We determined that a serving size should be 10 milligrams of THC, and if you're going to eat something like a cookie ... the entire cookie should just be that one serving size of 10 milligrams, versus 100 milligrams and someone's required to break it into 10 pieces," Kilroy said.

Her office's phone still rings virtually every day with calls from newly legalized cities and states looking for input on regulation and standards. As the marijuana industry matures, and increasing amount of questions turn toward criminal justice and social equity. Denver itself is looking to expunge old marijuana convictions.

"When we look at marijuana convictions we understand that some of our low-income and minority communities have been disproportionately impacted by the war on drugs, and what can we as a city do to correct that," Kilroy said.

Another lane of trial and error? How to keep legal marijuana out of the hands of teens. As underage marijuana use drops, Kilroy points to the city pivoting away from D.A.R.E.-style programs.

"We know that the 'Just Say No' campaign did not work. Kids do not want to be lectured to. So we're giving them the facts and letting them make their own conclusions," Kilroy said.