As a growing number of states explore legalizing and taxing the sale of recreational marijuana, a new report cautions that revenue and economic benefit projections have been notoriously hazy.

The Pew Charitable Trusts on Monday published an analysis of how taxation and state revenues have fared in the 10 states, along with the District of Columbia, that have legalized recreational marijuana. To date, Alaska, California, Colorado, Maine, Massachusetts, Michigan, Nevada, Oregon, Vermont and Washington have all legalized recreational marijuana in some capacity.

The key takeaway, according to the report, is that states lack access to historical data and time-tested regulatory structures that would help analysts better predict how much of a boon the economic impact of the legal marijuana business could be.

"The biggest challenge for states has been a lack of information. It's notable that legalized recreational marijuana has only been sold in states since 2014," says Alex Zhang, a research officer at the Pew Charitable Trusts. "Several states underestimated how long it takes for the market to start running smoothly, whether that's getting businesses licensed and operational or getting products to market."

So-called "sin taxes" on products such as alcohol and cigarettes have historically been somewhat volatile but still more predictable in terms of revenue forecasting than the legalized sale of marijuana, according to the report, because consumers have been purchasing those other items for decades. With legal sales of recreational marijuana still relatively new, state budget experts have had a difficult time accurately predicting their impact, especially considering that longer-term users of marijuana will be transitioning from the black market to the legal one.

For example, revenues in Nevada were 40 percent higher than expected during the first six months of sales, Zhang says, while revenues were 45 percent below projections in California during its first six months.

The report notes that revenues have been solid in the first five states to legalize the sale of recreational marijuana now that a few years have passed. Tax collections "have been booming" in Colorado, Washington, Oregon, Alaska and Nevada. But the analysis goes on to note that "forecasters expect this growth to slow" going forward, with revenue growth leveling off in these states after the first couple of months of legalization.

"A piece of the consumer demand uncertainty that's pretty unique to legalized recreational marijuana is that there are so many different types of products on the market, all with different prices," Zhang says. "It's been a challenge for states to estimate how consumer preferences might shift between these product types. Colorado and Washington, for example, have seen edibles and concentrates become more and more popular."

Zhang also notes that, lacking federal guidelines, some cities and jurisdictions are pioneering their own taxation and regulatory format. Vermont and Washington, D.C., for example, are legalizing possession of recreational marijuana before they set up taxation guidelines and marketplace standards.

"California also requires local governments to set regulations, and that took additional time they may not have anticipated. And so all of these factors impact the number of businesses in the market, and that impacts sales and revenue generated from those sales," Zhang says.

That's not to say sales of marijuana haven't been beneficial to state budgets. Tax revenues from marijuana sales in Colorado earlier this year topped $1 billion . But Zhang recommends states considering legalizing and taxing recreational marijuana use the proceeds for one-time expenses or put them into a rainy-day fund.