The first licences in the United States that permit retailers to sell marijuana for recreational use from 1 January were issued in Colorado on Friday.

Owners of cannabis dispensaries lined up to collect the permits in Denver: an initial batch of 42 licences were issued, most to growers but around a dozen to shops.

Colorado voters approved a new law during the November 2012 general election that would expand the state’s laws allowing the production and sale of medical marijuana to cover recreational uses.

The owner of a Denver-based chain of medical marijuana dispensaries who wants to expand and sell pot to leisure consumers, Shawn Phillips, was first in line on Friday morning.

Phillips’s business, called Strainwise, will be able to sell cannabis to adults for both medical and purely recreational use from New Year’s Day.

The state already licenses more than 500 medical marijuana dispensaries, and only those outlets may apply to sell it for recreational use. State authorities have already approved 348 recreational sale licences but businesses also require a local licence, the first of which were those issued in Denver on Friday.

A festive atmosphere took over at the normally staid city licensing office in Denver on Friday. Justin Jones of Dank Colorado in Denver picked up his s grower’s and retailer’s licences for recreational pot on Friday to add to his newly-acquired state licence in readiness for expanding his medical business for recreational purchases on 1 January.

Jones said his most popular product was a strain called Space Queen. “It’s a relaxing, mellow high that you feel through your whole body from head to toe,” Jones told the Guardian He argued that pot users are an “intelligent community” and the change in the law would not lead to binge smoking and trouble in 2014.

“Most people have been doing this illegally for so long that they are just ready to celebrate the fact that they can now purchase marijuana legally. I look forward to ending this version of prohibition,” he said.

Colorado last year also brought in a new law specifically to cover the offence of driving under the influence of drugs, which sets a limit of 5 nanograms of the active ingredient in cannabis, THC, in the blood while operating a vehicle.

Jones said it was not yet clear how individuals, especially newcomers to marijuana, would adapt to the law and work out how much pot they could consume without being over the limit. There is no breath-test for drivers who are high on cannabis, they have to give a blood sample.

“We are waiting to see how the science works out. We are waiting to see how many elements of the new law will pan out,” he said.

He said he hoped employers who currently have a zero tolerance policy on drug use among their workers would “adapt to the cultural changers” now accelerating in Colorado.

Colorado’s Marijuana Enforcement Division spokeswoman Julie Postlethwait explained that the laws do not permit consumption of marijuana in public in any form nor on the premises of dispensaries in California-style pot cafes. “You buy it and take it to your private property to consume,” she told the Guardian.

After voters approved recreational sale and use, the state legislature drew up the details of the laws and passed the necessary legislation last June, to come into force on 1 January 2014.

Local authorities have been able to pass bans or temporary stays on following the laws in their town or county, pending further local votes or any legal challenges.

The mountain town of Boulder initially decided on a local ban on the sale of marijuana for recreational use despite the town having several medical dispensaries, but has since relented.

The ski resort of Breckenridge decriminalised the possession of small amounts of cannabis and consumption in private for recreational use several years ago. That decriminalisation will now apply across the state, regardless of whether local towns or counties ban the actual sale of the substance in their area by refusing to issue local growing or sale licences.

The sale and possession of cannabis is still prohibited in Colorado by federal law, for either medical or recreational use, putting the state in a head-on clash with Washington. But there is no evidence yet that the federal authorities plan to enforce the law in areas that have voted to relax it locally.