This article was updated on August 4, 2017, and originally published on March 27, 2017. 

Seemingly nothing can stop the marijuana industry, or marijuana stocks, at the moment.

Over the past couple of years, we've witnessed a number of major milestones for the cannabis industry. For example, in 2012, Colorado and Washington became the first states where a majority of voters legalized the sale of recreational marijuana to adults ages 21 and up. Since then, an additional six states have joined in. The rapid growth in legal recreational weed sales is what helped push Colorado to more than $1.3 billion in legal marijuana sales (medical plus recreational) in 2016. Comparatively, legal sales only hit $996.2 million in 2015.

Another interesting milestone involves Ohio and Pennsylvania. The legislatures of both states wound up directly legalizing medical marijuana in 2016, which could pave a path for other legislatures to save time and follow their lead.

Marijuana buds in a jar sitting atop a pile of cash.

Image source: Getty Images.

The largest marijuana stocks have skyrocketed over the past year

This rapid growth in legal pot has created quite the demand for marijuana stocks. The seven largest marijuana stocks by market cap have all put on a show over the past couple of years. Here are those seven "green giants" listed with their market caps as of August 4, 2017, along with their trailing one-year total returns.

  • GW Pharmaceuticals (NASDAQ:GWPH): $3.0 billion, up 25%
  • Canopy Growth Corp. (NASDAQ:CGC): $1.1 billion, up 136%
  • Aphria (NASDAQOTH: APHQF) $630 million, up 136%
  • Aurora Cannabis (NASDAQ:ACB): $653 million, up 338%
  • AXIM Biotechnologies (OTC:AXIM): $389 million, up 2,180%
  • Corbus Pharmaceuticals (NASDAQ:CRBP): $306 million, up 112%
  • Medical Marijuana (OTC:MJNA): $189 million, up 85%

As you can see, these are some hefty valuations -- and some exceptionally strong moves higher on the heels of marijuana's expansion. With the exception of GW Pharmaceuticals and Medical Marijuana, the other five largest marijuana stocks have at least doubled in value over the trailing 12 months, with cannabinoid-based drug developer AXIM Biotechnologies skyrocketing more than 2,000%!

Some of you might also be wondering why I've excluded Insys Therapeutics from this list. Despite the Food and Drug Administration approving Syndros, the company's oral dronabinol solution, in July 2016, it still generates practically every cent in revenue from sublingual drug Subsys, which has nothing to do with cannabis. Calling Insys a marijuana stock is a bit of a misnomer, and as such, I've chosen to exclude it, for the time being.

A person using a magnifying glass to examine a company's balance sheet.

Image source: Getty Images.

A "doobie-ous" similarity among marijuana stocks

However, these marijuana stocks have another similarity that goes beyond their growing market caps and their exceptional trailing-one-year performances. They all possess an astronomically high price-to-sales ratio, because all seven of these companies have very little in the way of sales to speak of.

Below, you can see the trailing-12-month revenue totals for all seven of the largest marijuana stocks: 

  • GW Pharmaceuticals: $10.11 million
  • Canopy Growth Corp.: $22.92 million
  • Aphria: $15.43 million
  • Aurora Cannabis: $10.12 million
  • AXIM Biotechnologies: $0.05 million
  • Corbus Pharmaceuticals: $2.81 million
  • Medical Marijuana: $14.07 million

Combined, these seven marijuana stocks with an aggregate valuation of $6.3 billion have generated a cumulative $79.3 million in sales. That's a frighteningly bad figure for fundamentally focused investors. Here's a closer look at each company's current price-to-sales ratio.

  • GW Pharmaceuticals: 288.42
  • Canopy Growth Corp.: 33.62
  • Aphria: 33.01
  • Aurora Cannabis: 42.06
  • AXIM Biotechnologies: 6434.56
  • Corbus Pharmaceuticals: 94.09
  • Medical Marijuana: 10.32

Admittedly, some of these figures are high because a few of these marijuana stocks are clinical-stage drug developers. Nonetheless, only GW Pharmaceuticals, with its $3 billion valuation, is anywhere close to bringing a strong-selling cannabinoid-based drug to market (its cannabinoid-based drug Sativex is already on the market in Europe, but with minimal annual sales).

Cannabis plant in a lab next to test tubes.

Image source: GW Pharmaceuticals.

In two phase 3 trials each for Lennox-Gastaut syndrome and Dravet syndrome, two rare forms of childhood-onset epilepsy, GW Pharma's experimental cannabinoid-based drug Epidiolex easily met its primary endpoint of a statistically significant reduction in seizure frequency. Though a cannabinoid-based drug is not guarantee to be approved by the Food and Drug Administration, it's certainly on the right path to reaching pharmacy shelves. Epidiolex could easily surpass $1 billion in peak annual sales if approved, possibly allowing the company's aggressive valuation to make sense.

The remaining drug developers, including Corbus Pharmaceuticals and AXIM Biotechnologies, are still years away from potential commercialization of their drug pipelines.

Additionally, only Aurora Cannabis, among the seven marijuana stocks listed above, reported a profit in its most recent quarterly results. 

Long story short, cannabis stocks appear to be grossly overvalued on a fundamental basis.

It gets worse

But wait -- there's more.

Donald Trump speaking to Department of Homeland Security employees.

Image source: U.S. Department of Homeland Security, Flickr.

In addition to investors probably allowing their emotions to get the better of them when investing in marijuana stocks, they may have overlooked the chilling warning sent from now-former White House press secretary Sean Spicer in February. Spicer indicated that the Trump administration plans to beef up its enforcement of federal marijuana regulations. The good news is that it doesn't look as if medical marijuana is in the crosshairs of the Trump administration, but any chances of recreational marijuana expansion in the U.S., along with an easing of restrictions on the industry, probably went right out the door.

For instance, cannabis businesses have very minimal access to basic banking services, meaning most don't have checking accounts or the ability to open a line of credit. Banks often report to the Federal Deposit Insurance Corporation, which is, in turn, an independent agency created by Congress. Banks that offer basic banking services to cannabis businesses could be accused of money laundering by the federal government. And so, few banks take that risk, as unlikely as it might be.

Pot companies also get an unfair shake come tax time. U.S. tax code 280E disallows businesses that sell federally illegal substances from taking normal tax deductions, thus burdening marijuana businesses to pay tax on their gross profit as opposed to net profit.

These are all red flags for investors that should keep them out of marijuana stocks and planted firmly on the sidelines.

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.