When it comes to top-performing industries, you'd have a tough time surpassing the returns of marijuana stocks. Of the 13 marijuana stocks with a market cap in excess of $200 million, over half have more than doubled in value over the trailing year.

Here's why marijuana stock investors are seeing green

Why such bullishness for pot stocks? Look no further than rapidly changing public perceptions of cannabis, and legal weed sales growth.

A tipped over bottle of cannabis buds on a pile of cash.

Image source: Getty Images.

National pollster Gallup has been keeping tabs on the public's opinion of marijuana for nearly five decades. Back in the mid-1990s, marijuana wasn't all too popular, with just 25% of the public calling for its nationwide legalization. As of 2016, an overwhelming 60% of the public now wants to see cannabis legalized, which represents an all-time high.  Also, a separate poll from Quinnipiac University found that 94% of respondents in its survey wanted medical cannabis legalized across the United States. Long story short, investors believe this changing tide of opinion could force the hands of lawmakers in Washington to make changes to federal marijuana laws, or risk being voted out of office.

Legal sales growth has also lured in marijuana stock investors. According to leading cannabis research firm ArcView, North American legal weed sales grew by 34% in 2016 to $6.9 billion, and they're forecast to grow by 26% per year through 2021. If this projection from ArcView turns out to be correct, the legal pot market in North America will have tripled in value in just five years to nearly $22 billion. It's incredibly difficult for investors to find industries with that sort of consistent growth, which is why marijuana stocks have attracted so much money of late.

Now that's what I call a capital gain!

However, two marijuana stocks really stand out from the crowd. If you had invested $10,000 in either of the two top-performing marijuana stocks, you'd now have a respective $125,000 and $300,000! That's not chump change considering that the stock market has historically gained only 7% per year, inclusive of dividend reinvestment. Let's have a look at these pot stocks, which appear to be headed in diverging directions.

Cannabis leaves sitting next to biotech lab testing equipment.

Image source: GW Pharmaceuticals.

GW Pharmaceuticals: $10,000 to $125,000 in just over four years

Within the realm of marijuana stocks, there's GW Pharmaceuticals (NASDAQ:GWPH) and everyone else. GW Pharmaceuticals has the highest market cap of any marijuana stock -- at least one that devotes a majority of its business to cannabis or drug-based cannabinoids -- at more than $2.8 billion. And since the summer of 2013, its share price has risen from about $9 to a recent $112 a share, which would have netted investors a cool $125,000 had they invested $10,000 and hung on for the ride.

GW Pharmaceuticals' future is definitely looking up, thanks in large part to the success in clinical trials of experimental drug Epidiolex, which is a cannabidiol-based oral solution for two rare types of childhood-onset epilepsy, Dravet syndrome and Lennox-Gastaut syndrome. In two pivotal-stage studies for each indication, Epidiolex led to a statistically significant reduction in seizure frequency, setting its lead drug up for what could be an approval from the Food and Drug Administration (FDA). 

It's really tough to gauge what sort of peak annual sales potential Epidiolex could have given that it's cannabinoid-based, but anywhere in the $500 million to $1 billion range seems achievable. Of course, this is pending approval from the FDA, and assumes that Epidiolex is priced and launched successfully, and has a shot at label expansion in the future. GW Pharmaceutical still has much to prove after the previously unsuccessful launch of spasticity-reducing therapy Sativex for multiple sclerosis patients in European markets, but the company looks to be on the right track with Epidiolex.

A magnifying glass being held over a balance sheet.

Image source: Getty Images.

Axim Biotechnologies: $10,000 to $300,000 in less than a year

On the other hand, the top-performing marijuana stock might also be the most hazardous to investors' wealth. Axim Biotechnologies (OTC:AXIM), which was valued at anywhere from $0.21 to $0.25 a share less than a year ago, now finds its share price north of $7 (and at one point it was approaching $20). Had investors purchased $10,000 of Axim's stock last September, they would have $300,000 (or perhaps even a tad bit more) as of today.

The buzz around Axim is similar to that of GW Pharmaceuticals: the opportunity to use cannabinoids to effect positive biologic change. But there's a pretty key difference between the companies. Whereas GW Pharmaceuticals is well-funded and has multiple successful late-stage studies in its back pocket from Epidiolex, Axim's more than one dozen clinical trials listed on its website are mostly conceptual at this point. There's been very little in the way of dose-finding and safety studies conducted, meaning investors have been essentially buying blind. This isn't to say that Axim's delivery methods, such as cannabidiol-based chewing gum, suppositories, or cannabinoid-infused gels, aren't exciting, rather it points out that there's been very little presented thus far to signify that Axim is worth anywhere near its $385 million valuation.

What's worse is that Axim is a going concern, according to its auditors. It ended the previous quarter with less than $600,000 in cash on hand, negative working capital, and it currently doesn't have the funding to complete its clinical objectives. That's not good, and there's probably not an amicable solution for investors short of common stock dilution.

If there's a very clear marijuana stock worth avoiding, this Fool would suggest you steer very clear of Axim Biotechnologies.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.