Penny stocks, defined as equities that trade at less than $5 a share, are rarely worth the risk. Companies with extremely low share prices tend to have weak balance sheets, an absurdly high number of outstanding shares, few institutional investors, sky-high levels of interest from short-sellers, and a poor near-term outlook. What's more, these types of equities are often used as day-trading vehicles, making them exceptionally volatile in terms of price.

All of that said, there are a select few penny stocks worth buying right now. In fact, these hidden gems may even make their early shareholders rich by the end of the current decade.    

Which penny stocks stand apart from the crowd? Adaptimmune Therapeutics plc (NASDAQ:ADAP) and OrganiGram Holdings Inc. (NASDAQ:OGI) are two healthcare stocks that sport jaw-dropping levels of deep value -- most of which is being completely ignored by this moody market right now.

Here's a brief rundown on why these top penny stocks could be big winners for patient investors.

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Adaptimmune: A T-cell focused immuno-oncology company

Adaptimmune's shares have been on fire this year, and for good reason. In January, the company announced that its unique T-cell therapy platform delivered initial responses to four solid tumor indications. Not long afterwards, Adaptimmune executed a secondary offering to shore up its balance sheet, and it inked a broad collaboration deal with Japanese pharma titan Astellas Pharma.

This Astellas deal comes with a $50 million upfront payment, a favorable royalty agreement, and the potential for hundreds of millions in additional clinical/regulatory milestone payments. Last but certainly not least, Adaptimmune also announced earlier this year that its synovial sarcoma treatment ADP-A2M4 remains on track for a 2022 commercial launch. 

What's the big deal? Adaptimmune's market cap of just $391 million comes across as downright absurd in light of the enormous value proposition of its clinical pipeline. Investors have cooled their heels on cell-based cancer therapies in general thanks to the various logistical issues associated with their commercialization, along with their well-known safety problems. As a result, the current generation of FDA-approved T-cell therapies have failed to come anywhere close to their former peak sales estimates -- and they may never do so.

However, Adaptimmune doesn't necessarily need a mega-blockbuster product to create tremendous returns on capital for shareholders. In effect, ADP-A2M4 only needs to generate perhaps $100 million in annual peak sales to be a major growth driver for the company. This initial therapy, combined with the Astellas collaboration, should be more than enough to cause the company's shares to at least double within the next four quarters.

Longer term, Adaptimmune has the clinical assets in place to produce some mind-boggling returns for early shareholders.  

OrganiGram: A grossly undervalued cannabis company

Cannabis stocks have gotten absolutely crushed over the past 12 months. Investors are fleeing this emerging industry because of a variety of headwinds such as poor earnings, managerial missteps, ever-rising tax rates, bureaucratic red tape, and a host of scandals. Nonetheless, the legal cannabis industry is still expected to eventually morph into a $50 billion a year space, and it may even hit the $200 billion mark by the end of the decade. So, there is a solid rationale for owning one or more of these beaten-down equities for the long haul. 

Canada's OrganiGram, in many respects, may be the best of the bunch. OrganiGram's stock has shed nearly two-thirds of its value over the prior 12 months. But the company's sinking valuation had little to do with its internal operations or financial performance during this period. Rather, OrganiGram's stock was simply caught up in the wave of selling across the industry. The company's sharp pullback, though, may have created a once-in-a-lifetime buying opportunity for savvy investors.

The key reason is that OrganiGram has been one of the few major pot growers to run its business as a consumer packaged goods company right from the jump. In short, the company has placed a premium on growing great weed in a cost-efficient way since its inception. The net result is that OrganiGram has one of the lowest costs of production, a better-than-average balance sheet, and a well-earned reputation as a top-level grower. Many of OrganiGram's peers, by contrast, are now facing serious liquidity issues because of their overly aggressive expansion plans. 

Bottom line: If you're looking for a vehicle to gain exposure to the high-growth cannabis industry, OrganiGram is probably your best bet. The company's shares are presently trading at less than two times forward-looking sales, which is a dirt-cheap valuation for a high-level cannabis company with solid fundamentals. 

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.