It isn't that hard to double your money if you're patient. If you had sunk money into an ETF that tracks the S&P 500 at the beginning of 2013, you would already have accomplished this feat without risking much in the process.

Developing new drugs to treat severe diseases can lead to overnight riches, and losses. These three biotech stocks could double impatient investors' money in the not so distant future if those investors don't mind accepting a great deal of risk. Here's how these three fledgling drugmakers will try to make it happen for their shareholders.

Cash money raining down on a guy in a suit.

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Galectin Therapeutics, Inc.: NASH underdog 

Galectin Therapeutics' (NASDAQ:GALT) has a new drug candidate that failed to hit its main goal in a clinical trial, but it smashed through an unexpected one that looks kind of important. Galectin's cryptically named candidate, GR-MD-02, significantly reduced the throat blisters that often develop in patients with cirrhosis caused by non-alcoholic steatohepatitis (NASH) during a mid-stage trial.

Cirrhosis-damaged livers tend to push up venous pressure in a way that leads to painful blisters, called esophageal varices. Among 107 patients treated with GR-MD-02, just one developed new varices. In contrast, six patients in the 54-patient placebo group developed new varices.

Unfortunately, Galectin set out to prove its candidate could reduce patients' hepatic venous pressure gradient (HVPG). Investigators measured an HVPG difference, but it wasn't strong enough to be considered statistically significant.

After meeting with the FDA, Galectin decided to start a pivotal trial with two primary endpoints, then choose one most likely to succeed following an interim assessment. Put mildly, altering your primary endpoint in the middle of a clinical trial is frowned upon.

While the dual primary endpoint is troubling, there are around 260,000 NASH cirrhosis patients in the U.S. and EU without esophageal varices that would like to prevent them from forming. If GR-MD-02 can't become the first NASH cirrhosis treatment, it could have a modest future simply preventing the associated blisters.

Prescription drugs stacked in shape of upward sloping chart.

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Right now, Galectin Therapeutics is small enough that investors could double their money if the company can begin recording modest drug sales in the years ahead. The company's market cap is only $205 million at recent prices and biotech stocks tend to trade at mid-single-digit multiples of their total annual sales.

Geron Corporation: Looking for commitment

Geron Corporation (NASDAQ:GERN) is trying to get its only candidate picked up by its big pharma partner, Johnson & Johnson (NYSE:JNJ). Right now, the partners share costs for development of an experimental blood cancer treatment called imetelstat, which has a somewhat checkered past. Investors willing to accept a great deal of risk could see this stock double if stellar top-line results from the IMbark trial convince J&J to pick up the tab for larger, more expensive, pivotal studies.

Using a cut-off date in April, investigators are checking for an overall survival benefit among myelofibrosis patients treated with imetelstat. If they find one, a lucrative deal with the world's largest healthcare company seems imminent. Right now these patients' treatment option is limited to Jakafi, which raked in $1.1 billion last year.

Progenics Pharmaceuticals, Inc.: Relieving pressure

Progenics Pharmaceuticals, Inc. (NASDAQ:PGNX) is eagerly awaiting an approval decision that the FDA is expected to hand down by the end of July. Investors are a little nervous because the agency delayed Azedra's decision earlier this year to allow for a late addition of some non-critical information.

If approved, Azedra would become the first available treatment for two rare forms of cancer that affect the adrenal glands and often cause sky-high blood pressure. During a trial underpinning Azedra's application, patients were able to control their blood pressure with less help from other drugs. More importantly, patients that were treated with two doses survived more than twice as long as those given a single dose.

Pills on top of cash.

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Right now, Progenics sports a modest $558 million market cap that could double if Azedra eventually becomes standard care for patients with pheochromocytoma and paraganglioma. If approved, gaining popularity could take some time, which Progenics has plenty of.

Why this one's my favorite

Geron and Galectin could double, but they could also get pounded flat if their lead candidates suffer any mishaps. Progenics, though, can depend on a modest revenue stream from Relistor, plus it has a prostate cancer imaging agent entering late-stage development. Relistor's a drug for opioid-induced constipation that doesn't exactly make ends meet for Progenics, but it has limited the company's losses to $48 million over the past year. 

Progenics finished March with around $87 million in cash, and Azedra's aimed at a small, but highly motivated population. If this small biotech needs to tap investors for more capital to launch it successfully, it probably won't need much.

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.