Call it a drug trade for investors. Todd Harrison, CEO and founder of Internet-based financial media company MInyanville, thinks cannabis "will be the single best investment idea for the next ten years."

Related: Pot Pushback Goes Up in Smoke: $20 Billion Economy Awaits Marijuana Legalization

But while the public has watched recreational marijuana take off in Colorado this year, how can they profit from it as an investment theme?

Harrison believes it will be driven by the broader legalization of marijuana, inspired by states' need for tax revenue. He points to expectations that legal marijuana use is expected to generate $134 million in tax revenue for the upcoming fiscal year in Colorado, the first state to allow recreational marijuana. That's nothing to sneeze at, and Harrison calls the state the "litmus test" for broader legalization. Harrison also cites the expected decline in crime rates and prison populations as powerful incentives to decriminalize marijuana.

Related: Post Office Looking Into Shipping Beer, Wine & Liquor But Not Marijuana

The New York Times reports that half the states in the U.S., including some in the conservative South, are currently considering decriminalization of the drug or legalizing it for medical or recreational use. Oregon and Alaska are the likeliest to legalize pot next year. Twenty states now permit the use of medical marijuana now, while Colorado and Washington have legalized it for recreational use.

Related: “Marijuana Is a Vegetable” and Belongs in the Farmers’ Market: Pot VC

The legal marijuana market is estimated to grow 64% to $2.34 billion in 2014 from $1.44 billion, according to a recent report by the cannabis investment and research firm Arcview Group.

Wall Street currently doesn't cover the marijuana market as an industry but once legalization is more widespread, that will be the inflection point when we marijuana investing moves mainstream, says Harrison.

Currently the chatter is mostly about marijuana penny stocks. They are not what Harrison is talking about. He says those stocks are very risky and volatile, and he doesn't touch them.

But there are some "real" companies generating interest. Harrison cites the cannabinoid prescription medicine company GW Pharmaceuticals (GWPH) as an example. He's not suggesting the stock as a buy or sell, just as an example he's traded in the past. The stock has rallied more than 500% since last summer.

Advanced Cannabis Solutions (CANN), soared 62% in a single day when its stock chart was shown on CNBC earlier this week -- even though it was a mistake, and the anchor was actually discussing another company in the cannabis industry, called CannaVEST (CANV). Advanced Cannabis Solutions leases growing facilities to legal marijuana growers and dispensary operators. CannaVEST makes hemp-based consumer products. (CORRECTION: An earlier version of this story said that Advanced Cannabis Solutions soared 62% in a single day when it was mentioned on CNBC earlier this week.)

"That's more bearish than bullish," says Harrison, reminding him of the bubble levels reached back in Y2K days.

The comparison could cause would-be investors to bristle. Harrison says it's about investors' time horizon and risk tolerance. In the bubble of Y2K, everyone was excited about the Internet, he says, and everything they expected the Web to be proved true, but not until after the tech crash.

Harrison says investors should expects ebbs and flows in the marijuana industry. He sees a 10-year horizon with tremendous opportunity that will not be without "potholes, false starts and a lot of risk." The moral of the story is to do your homework.

Others are more skeptical. Bloomberg reports Mark A.R. Kleiman, professor of public policy at the University of Southern California at Los Angeles, doesn't "see how there's money to be made producing an agricultural commodity," which marijuana is, because once the market becomes competitive, prices will fall.

Other investors recommend avoiding these stocks until marijuana is legal throughout the U.S. Federal law still says marijuana is illegal, though the Obama Administration has said it won't interfere with the rollout of legalized cannabis in individual states. And though the federal government has said that bankers following Treasury guidelines in providing services to cannabis companies operating in those states won't face prosecution, many large banks still won't process funds earned from pot sales.

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