Did Coloradans legalize the retail sale of marijuana mainly to serve tourists and visitors?

You begin to wonder after reading a state study on “Market Size and Demand for Marijuana in Colorado” and scouring the latest tax-collection reports.

It’s not just that 90 percent of retail sales of marijuana in mountain resorts so far have been to out-of-staters, as well as almost half of all such retail sales in the state and 44 percent of those sales in the Denver metro area. Many of Colorado’s heaviest marijuana users, meanwhile, appear to be quite happy sticking with medical pot, which they were able to obtain long before Amendment 64.

Medical pot is cheaper (7.62 percent sales tax in Denver as opposed to 21.12 percent at retail outlets) and more widely available. And while it requires a doctor’s permission, that has been notoriously easy to secure.

Heavy users — those who consume marijuana every day — “drive almost 70 percent of total marijuana demand,” the Department of Revenue study says. No wonder medical marijuana sales dwarfed retail sales in the first four months of this year — $133 million vs. $70 million — while tax revenues from retail pot are lagging far behind projections.

Ninety-four percent of medical pot users cite “severe pain” as their condition. You too might discover severe pain requiring treatment if your marijuana habit was costing so much.

“It was initially thought that medical marijuana patients would purchase marijuana in the retail market, but it is increasingly clear that this conversion will not occur as long as the large price differential persists and as long as retail marijuana is not available in as many jurisdictions as medical marijuana,” the state study concludes.

But if medical marijuana patients aren’t converting in Denver, where retail pot is readily available, why should we suppose they will convert anywhere else given more retail shops?

Price and availability may not be the only reasons for medical marijuana’s unexpected resilience, either. The fact that medical and retail pot establishments are allowed to co-locate on the same premises — in apparent violation of Amendment 64 — no doubt has propped up medical sales, too.

It’s all but forgotten now, but the amendment passed in 2012 said, “Nothing in this section shall be construed to permit any medical marijuana center … to operate on the same premises as a retail marijuana store.”

And yet thanks to the legislature’s decision to flout the constitution, co-location is actually the norm.

The governor’s task force on Amendment 64 last year recommended “complete” physical separation between the two types of stores, but lawmakers approved rules saying medical and retail shops could share the same space so long as there were no sales of medical marijuana to patients under 21.

The result in Denver, according to the city’s executive director of marijuana policy, Ashley Kilroy, is that 85 of the city’s 90 retail stores sell both medical and retail pot, and just 21 have separate entrances and facilities.

Given this state of affairs, dreams of a tax bonanza from retail marijuana may have to be put on hold. Heavy users drive marijuana sales and they have a strong incentive to use cheaper medical marijuana. And marijuana store owners have no incentive to convert solely to retail sales given the convenience of operating both types of outlets.

But at least we’ve made the tourists happy with our new retail shops.

E-mail Vincent Carroll at vcarroll@denverpost.com. Follow him on Twitter @vcarrollDP