Medical marijuana stocks are smoking now that an increasing number of states are voting for legal marijuana or the legalization of cannabis — but even the best marijuana stocks also come with plenty of risks.

As part of a brand-new industry, marijuana stocks are, shall we say, immature. The best, most heavily traded options for medical marijuana stocks all trade over-the-counter. As penny stocks, medical marijuana stocks aren’t subject to the same regulatory scrutiny or listing requirements of stocks trading on a major exchange like the Nasdaq or New York Stock Exchange.

As always, buyer beware — but it wouldn’t hurt to be extra careful when it comes to investing in over-the-counter medical marijuana stocks.

Be that as it may, the burgeoning legal marijuana industry will surely make big winners of some medical marijuana stocks. And tapping the equity market for the capital to grow a medical marijuana business could give these companies a competitive edge.

Furthermore, as penny stocks, medical marijuana stocks will be extremely volatile. That increases the risk that you’ll buy high and sell low — but it also means medical marijuana stocks could generate 10-bagger returns.

So if you are looking for the best marijuana stocks, these are the most established options.

Best Marijuana Stocks: Medical Marijuana Inc. (MJNA)

11/20 Stock Price: 12 cents

Market Cap: $109 million

YTD Performance: 14%

One of the best marijuana stocks to consider for betting on the legalization of cannabis is Medical Marijuana Inc. (MJNA). That’s because MJNA stock is one of the more heavily traded marijuana stocks, with an average of 6.2 million shares trading hands each day.

As a comparison, GreenGro Technologies (GRNH) does less than 10% of that volume.

Medical Marijuana Inc. runs a portfolio of companies, including CanChew, PhtyoSphere and Canipa Holdings. The companies engage in everything from developing a cannabinoids gum to expanding the presence of MJNA in Europe.

Shares in Medical Marijuana Inc. are up 14% since the start of the year. But as is true with most penny stocks, MJNA has been very volatile. Medical Marijuana Inc. started the year at 10 cents then jumped to break above 45 cents by mid-February. Yet MJNA stock has been trending down ever since.

For the most recent quarter, sales for MJNA were only about $600,000, down from $3 million a year ago, as Medical Marijuana Inc. continues to rack up operating losses.

Best Marijuana Stocks: Growlife (PHOT)

11/20 Stock Price: 7 cents

Market Cap: $41 million

YTD Performance: 79%

Another more-established of the marijuana stocks is Growlife (PHOT), as PHOT stock trades over 13 million shares per day. Like Medical Marijuana Inc., Growlife is a holding company for a line of legal marijuana businesses, in this case catering to growers.

In fact, the most recent claim to fame for PHOT is the introduction of the first kiosk-based payment and compliance system for legal marijuana dispensaries.

As an allied play on legal marijuana, shares in this medical marijuana stock have really taken root in 2013. Growlife stock is up almost 80% for the year-to-date, but like all medical marijuana stocks, it’s very volatile. Shares of PHOT stock have traded in a range of 1 cent to 10 cents a share.

For the most recent quarter, Growlife had a loss of $1.6 million on revenue of $865,000, and it claimed $83,000 in cash and cash equivalents on its books.

Best Marijuana Stocks: Cannabis Science (CBIS)

11/20 Stock Price: 3 cents

Market Cap: $24 million

YTD Performance: -34%

Cannabis Science (CBIS) is probably the most “medical” of all medical marijuana stocks. It’s led by Dr. Robert Melamede, a leading scientist in the field of cannabinoid research.

As such, Cannabis Science looks more like a biotech or pharma company than the rest of these marijuana stocks, since it seeks to develop cannabinoid-based products for approval by the Food and Drug Administration.

So far, that hasn’t been a very good bet for investors. Shares of CBIS stock are off 34% for the year-to-date, and — again — like all medical marijuana stocks, they are volatile. Cannabis Science stock was actually up about 90% back in February.

CBIS had no revenue in the most recent quarter and a loss of $928,000. As a result, Cannabis Science is looking for additional capital to stay afloat. Still, CBIS stock makes this list because it’s also more heavily traded than some smaller marijuana stocks.

Best Marijuana Stocks: MediSwipe (MWIP)

11/20 Stock Price: 18 cents

Market Cap: $7.8 million

YTD Performance: 15%

MediSwipe (MWIP) is another medical marijuana stock that’s an allied play on legal marijuana. MediSwipe facilitates the medical marijuana business by providing electronic transaction processing and accounts receivable financing, among other services.

Shares of MWIP stock have been volatile even for a medical marijuana stock. MediSwipe is up 15% for the year-to-date, but at one point the stock was up as much as 600%. However, unlike PHOT or CBIS, it never went negative this year.

For the most recent quarter, MediSwipe had a net loss of $182,000 on revenue of $47,000. However, cash and cash equivalents grew to $153,000 from $1,892 at the end of last year. And while MWIP stock trades just under 5 million shares per day, its $7.8 million market cap is still much larger than other marijuana-related stocks like CannaVest Corp (CANV), for example.

The bottom line: Proceed with caution if you’re looking to bet on marijuana stocks, or any penny stocks. But if you’re really a big believe in the legal marijuana megatrend, these are the most established names in the space.

As of this writing, Dan Burrows did not hold a position in any of the aforementioned securities.