The International Cannabis Business Conference in San Francisco, California drew in hundreds of marijuana enthusiasts for its opening day on 15 February.

The conference is an opportunity for attorneys, entrepreneurs and other professionals to network and consider the future of marijuana in the US as well as in California.

"We know that cannabis is America's number one cash crop, more than corn. Yet it's illegal, okay. So now as cannabis becomes legal this number one cash crop is now being regulated and taxed," said Alex Rogers, the executive producer of the conference. Rogers is also the founder of two medical marijuana clinics in Oregon.

Some 23 states and the District of Columbia permit medical marijuana use, though the drug remains illegal under federal law. The legalisation of the drug is well underway in North America following 2014 ballot victories in Oregon, Alaska and the District of Columbia, which joined Colorado and Washington in allowing adults to use the drug without a prescription.

On 10 February, marijuana advocates filed paperwork in Maine seeking a 2016 ballot initiative that would legalise recreational use of the drug in the north-eastern-most state.

The push for legalisation is creating a growing interest in the economic profits of cultivating and selling marijuana.

"So what we're investing in is we're helping marijuana business owners connect up with the sources of capital they need to take their one or two or three store business and turn it into eight, 10, 12, 15 stores" said Scott Jordan, an investor with the Colorado based company Dynamic Funding.

In the first four months of 2014, marijuana sales in Colorado amounted to more than $202m (£131m), about a third of them recreational. Taxes from recreational sales were almost $11m.