With more states voting to legalise the product, a once criminal activity is fast entering the mainstream with financial institutions, advertisers, and blue-chip investment firms waking up to the wider possibilities of this flourishing industry.

Medical and recreational marijuana is now legal in 24 US states, with a further nine due to vote on legalisation over the course of this year.

Colorado was the first state to open up legal marijuana sales in 2014, and reported $1bn (€890m) in sales of the product last year.

More tellingly, the state’s tax take on marijuana is now double that of alcohol — a fact that has made every other state sit up and take notice of the potential revenue bonanza waiting to be tapped.

Retail sales of recreational marijuana reached $4.5bn in 2015, up from $3.4bn in 2014 and $1.6bn in 2013. Analysts estimate the industry can reach $22bn by 2020.

With the public appetite for marijuana underlined by ever-upward sales graphs in those states that pioneered its legalisation, the early small-time investors in the fledgling industry are now being joined by a new generation of entrepreneurs keen to get in on the ground floor.

According to figures compiled by the 2016 Marijuana Business Factbook, the majority of marijuana companies are trading profitably — with 90% of operating dispensaries, recreational stores, and wholesale cultivators reporting stable or break-even status.

The cultivation and concentrates sectors are particularly lucrative, with 29% of wholesale growers ticking the “very profitable” box.

As the industry continues to grow, the number of financial institutions servicing its needs has increased to more than 300 this year, up from just 50 in 2015.

California, a potentially vast market, passed regulations last October to govern the industry, setting standards for local government, law enforcement, businesses, and health providers.

Over a million Californians already have physicians’ prescriptions to counter a range of conditions, including depression, cancer, and anxiety.

Unlike Colorado, which imposed strict regulations with licensed stores growing their own pot in enormous state-inspected warehouses, California’s recently formed Bureau of Medical Marijuana Regulation aims to open the entire marijuana supply line “from seed to sale” through legislation allowing for nurseries of up to an acre.

Like any fledgling industry, marijuana needs a persuasive public image to thrive into the future.

Earlier this month, a Colorado company announced its intention to bid for the naming rights for Sports Authority Field at Mile High, home of the Denver Broncos.

Concentrate company Openvape has submitted a proposal to rename the stadium ‘Openvape at Mile High’ — underscoring the industry’s efforts to harness innovative forms of mainstream marketing.

In a similar vein, the Dallas-based North American Cannabis Holdings recently announced the opening of a café in the Texas town of Frisco. Menu options will include custom-blended hemp-infused coffee, cold-pressed hemp smoothies, and raw hemp extract foods.

Legendary country singer Willie Nelson remains one of marijuana’s most vocal supporters, and recently announced the establishing of a company, Willie’s Reserve, with the aim of selling ‘Willie Weed’ across America.

A lifelong advocate of the herb, 83-year old Nelson says: “It’s just a matter of time before it gets legal everywhere in this country. I feel I bought so much, it’s time to start selling it back.”

Taking the product away from criminals is a constant theme of the singer’s: “Why should the criminals make all the money? Let’s tax it and regulate it, like we do with everything else and make some money off this,” he says.

Actor Jack Nicholson echoes the sentiment: “More than 85% of men incarcerated in America are on drug-related offences. It costs $40,000 a year for every prisoner. If they were really serious about the economy, there would be a sensible discussion about legalisation.”

While moves to legalise and commercially regulate any possible marijuana industry are still a long way off in Ireland, the Oireachtas Joint Committee on Justice, Defence and Equality has “strongly recommended” that the possession of small amounts of illegal drugs be decriminalised.

Former drugs minister Aodhán Ó Ríordáin, who referenced the Portuguese model where the decriminalisation of drugs for personal use passed in 2001 has resulted in police resources being concentrated on traffickers, said he was “in favour of removing the stigma compounded for those who end up with a criminal record due to possession of drugs for their own use”.