The marijuana industry is growing like a weed, and it's been putting smiles on the faces of marijuana stock investors. Of the one dozen largest marijuana stocks by market cap, a vast majority are up over the trailing year, and the average gain of those twelve is well over 100%. In other words, there's a really good chance that marijuana stock investors have been buzzing about their gains over the past year.

These impressive returns are a result of a rapid change in the public's opinion toward cannabis, as well as legal sales growth. Between 1995 and 2016, Gallup's periodic polling has shown that favorability toward legalizing marijuana has risen from 25% to an all-time record high of 60%. The higher this figure rises, the better the likelihood that lawmakers in Congress will consider taking action and adjusting pot's federal scheduling.

A cannabis plant growing in an outdoor commercial farm.

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In terms of sales, the "Marijuana Business Factbook 2017" from Marijuana Business Daily portends that U.S. sales will rise by approximately 300% between 2016 and 2021 to about $17 billion. That type of rapid, consistent, and long-term growth simply can't be duplicated, which is why investors have been so excited about legal weed's prospects.

Of course, its Schedule I status at the federal level, compounded with a high level of emotions among investors, has created a lot of volatility among pot stocks. Last week was among the tamest we've seen for marijuana stocks in a while. Nevertheless, one pot stock managed to tack on a double-digit percentage gain when all was said and done. This past week's budding performance belongs to clinical-stage drug developer Corbus Pharmaceuticals (NASDAQ:CRBP), which rallied by 16%.

Corbus Pharmaceuticals' catalyst last week is anyone's guess

What caused Corbus Pharmaceuticals' stock to rally so voraciously? One possibility is the company filing an 8-K with the Securities and Exchange Commission that notes it entered into a seven-year lease agreement with River Ridge Limited Partnership for its corporate headquarters in Norwood, Massachusetts. The long-term lease may portray confidence in future cash flow from management, as well as the likelihood of an expanding employee base, which in turn has investors excited.

Cannabis buds falling out of a tipped over white bottle onto a pile of cash.

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Another possible reason for Corbus' ascent could be Zynerba Pharmaceuticals' (NASDAQ:ZYNE) recent struggles with its lead drug, ZYN002. Though Zynbera and Corbus aren't direct competitors, the failure of ZYN002 as a treatment for focal seizures in adult epilepsy patients leaves the door open for another company to follow in GW Pharmaceuticals' footsteps as a leading cannabinoid or cannabinoid receptor-targeting drug developer. 

Lastly, we shouldn't discount the role momentum may have played. Sometimes short-term traders and emotions can move a company's share price without any clear catalysts, and that very well could be what happened last week.

What Corbus' shareholders should be monitoring

Despite last week's top-notch performance, Corbus Pharmaceuticals' shareholders would be wise to avoid lingering on their short-term gains and instead turn their attention to anabasum, the company's synthetic oral endocannabinoid mimetic drug currently being developed to treat systemic sclerosis, cystic fibrosis (CF), dermatomyositis, and systemic lupus erythematosus.

In terms of catalysts, investors are going to be privy to two critical events before the year ends. The company announced that it's planning to commence a late-stage study for anabasum in systemic sclerosis in the fourth quarter, and it's also planning to commence an extended phase 2b study involving anabasum in cystic fibrosis patients in Q4. 

A physician pondering what he's just read on a patients' clipboard..

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Though it has four indications it's targeting, CF is by far the most important from a revenue perspective. Whereas most CF medications target a specific mutation within CF, the belief is that anabasum, if effective, would work as a general anti-inflammatory for a majority of CF patients, regardless of their mutation. However, success in CF is far from a guarantee. In spite of producing a 75% reduction in the pulmonary exacerbation event rate compared to the placebo in a phase 2 study, anabasum failed to deliver any improvement in a key respiratory measure known as forced expiratory volume in the first second (FEV1). Other CF medicines on the market have delivered FEV1 improvement, throwing anabasum's effectiveness into question. A lot of Corbus' $340 million market is dependent on the success of anabasum in clinical trials.

For the time being, investors would be wise to remain on the sidelines until we have a better idea of how the CF studies will play out. Even missing out on an initial pop following a positive data release (assuming a positive outcome) should give long-term investors plenty of additional opportunities to make money. However, if anabasum flops in CF, Corbus' valuation could crater, and no one wants to be a shareholder if that happens. .

Sean Williams has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.