While small-cap stocks -- those with market caps between $500 million and $2 billion -- don't get as much attention as their large-cap cousins, there are plenty of promising investments in this area. Given their smaller sizer, these stocks have much more growth potential and are capable of multiplying in market value over a short period of time.

While there are hundreds, if not thousands, of small-cap stocks to chose from, not all of them are good investments. Here are three small-cap stocks that have tremendous upside potential over the near future.

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1. Portola Pharmaceuticals

Portola Pharmaceuticals (NASDAQ:PTLA) is a $1.9 billion biotech stock that has a drug candidate with serious blockbuster potential. The drug, called Andexxa, is an anticoagulant reversal agent, which essentially means it helps stop excessive bleeding in patients who are taking anticoagulants (also known as blood thinners).

There is tremendous demand for a drug that can stop the uncontrollable bleeding many patients on blood thinners experience. There were around 140,000 hospital visits in 2017 due to anticoagulant-induced uncontrollable bleeding, with many resulting in patient deaths. At the moment, there are no other anticoagulant reversal agents on the market, meaning Andexxa is the only drug that can address this issue.

Portola is putting Andexxa's price tag at $27,500 per patient dose, and when factoring in the 140,000 or so hospital visits of 2017, the American market for Portola's new drug would roughly be around $3.85 billion per year. With no other treatments on the market, investors can expect Portola's revenue to exponentially increase from the $36.8 million reported in Q3 2019, possibly reaching a figure in the billion-dollar range.

In terms of clinical development, Andexxa is in the clear. The Food and Drug Administration (FDA) has already approved the drug for commercial production in the U.S. alongside other prestigious designations, such as the important Breakthrough Therapy designation. Investors have a lot to look forward to from Portola in the years to come. 

2. NanoString Technologies

NanoString Technologies (NASDAQ:NSTG) is a small, $980 million market cap medical technology company that's done exceedingly well in 2019. With the stock having almost doubled since the start of the year, there's plenty of excitement behind NanoString -- and for good reason.

The company provides diagnostic equipment to laboratories, including technical instruments, diagnostic kits, and chemical reagents required for its other products (which it refers to as consumables). NanoString has pioneered some pretty novel technologies, such as its nCounter Analysis System, which lets scientists save time by analyzing a single tissue sample for hundreds of biological markers simultaneously. Without this technology, scientists would have to spend exponentially more time setting up tests, and they'd also need many more tissue samples from patients to execute the same number of tests.

NanoString's Q3 2019 revenue came in at only $30.6 million, and it reported a net loss of $22.8 million. While the company's management team is still focusing on pursuing a high-growth strategy, which means NanoString isn't expected to turn a profit anytime soon, it is expected to continue growing at a strong pace going forward. It is also worth noting that the bulk of NanoString's revenue came from consumables. Similar to how printer manufacturers also sell ink cartridges, these sales are a recurring source of revenue that will only continue to grow as more of its laboratory equipment is sold.

Although NanoString will stay a pretty niche business, when considering that it already commands a $1 billion market cap on its relatively small revenue figures, it wouldn't be surprising if NanoString's valuation shoots up by several times as the company's income grows.

3. Cara Therapeutics

Cara Therapeutics (NASDAQ:CARA) has been one of the most anticipated biotech stocks so far in 2019, although the company was hit by some unexpected news earlier in December. Cara's main drug candidate, a late-stage treatment called Korsuva, aims to treat patients with a type of reoccurring skin itch caused by kidney failure. Known as pruritus, this condition is especially prevalent among patients with late-stage kidney failure, with over 30 million people in the U.S. having been prescribed pain medication to deal with it.

At the moment, no drugs specifically treat pruritus. Instead, patients end up having to take opioids, corticosteroids, and antihistamines -- typical pain management drugs that often have their own side effects. However, Korsuva sets itself apart by the fact that it targets the peripheral nervous system to deliver pain relief. It doesn't have the same side effects or addictive properties as traditional pain drugs that target the central nervous system.

Clinical results have been strong for the most part. Korsuva's first phase 3 trial, Kalm-1, ended up a success, handily outperforming the placebo by a 20 percentage point margin in reducing itching symptoms. A second phase 3 trial, Kalm-2, is underway and expected to yield preliminary data sometime in early 2020.

However, a separate phase 2 trial for Korsuva surprised investors by failing to meet its secondary endpoints, although the primary target was still met by the trial. While the setback sent Cara's stock falling, in the grand scheme of things, missing the secondary endpoints for a single phase 2 trial isn't enough to derail what's already a promising drug candidate.

Cara Therapeutic's has a market cap of only $760 million at the moment, with Q3 2019 revenue of just $5.8 million. However, some analysts have estimated that Korsuva's peak revenue could reach as high as $570 million per year, although it's uncertain how quickly this could happen. With revenue figures that high, Cara Therapeutics' market value could easily multiply by several times on the low end should Korsuva end up receiving FDA approval, which seems more likely than not at this point.