What kinds of stocks hold the potential to double your money? Given enough time, nearly any stock could achieve the goal. But if you're looking for gains of 100% or more within a few years, you'll need to find growth stocks with huge market opportunities. Ideally, those stocks will have relatively small market caps that make the path to doubling easier.

I think three stocks check off all of these boxes. Here's why Guardant Health (NASDAQ:GH), The Trade Desk (NASDAQ:TTD), and Valens GroWorks (OTC:VLNCF) could double your money over the next couple of years.

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Image source: Getty Images.

1. Guardant Health

If you haven't heard of liquid biopsies yet, you will. They're blood tests that can detect cancer by identifying tiny fragments of DNA that break off from tumor cells. Liquid biopsies hold the potential to diagnose cancer at early stages when it can be more effectively treated. And Guardant Health ranks as the leader in liquid biopsies right now.

The company's Guardant360 product can detect non-small cell lung cancer as accurately as tissue biopsies and do so with a much shorter turnaround time. Clinical studies have also found that it's effective at detecting biomarkers used in establishing treatment plans for breast cancer patients. The GuardantOmni product is used by major drugmakers including AstraZeneca, Bristol-Myers Squibb, Merck, and Pfizer to in their development of cancer immunotherapies.

Guardant Health estimates that the addressable U.S. market for its two current products is around $6 billion annually. But that's just the beginning. The company's LUNAR liquid biopsies are only available for research use only right now but could target an addressable market of around $15 billion annually in monitoring for the recurrence of cancer plus more than $30 billion annually in screening and early detection of cancer.

The company's market cap currently stands at close to $8 billion thanks to its stock more than doubling this year. Even with the prospects for other liquid biopsies to enter the fray, Guardant Health could easily double again in the near future as its liquid biopsies gain wider adoption.

2. The Trade Desk

The Trade Desk is another stock that has more than doubled in 2019 and still has plenty of room to go much higher. The company provides a programmatic advertising platform used primarily by advertising agencies to purchase digital ads. Programmatic advertising enables advertisers and advertising agencies to use software to buy ads instantly instead of the old way of conducting lengthy negotiations with media outlets. 

How big is The Trade Desk's opportunity? Programming advertising should represent a market of around $34 billion this year. That's a drop in the bucket compared to the total global advertising market of around $725 billion. But that global market should increase to $1 trillion by 2025, with programmatic advertising comprising most of the market.

One of the biggest drivers of growth for The Trade Desk is connected TV (CTV) -- television connected to the internet. As you might expect, the popularity of ad-supported streaming services like Hulu have been a huge tailwind for the CTV market.

The explosion in the number of premium streaming services could very well lead to more ad-supported options for these services. That would open up an even bigger opportunity for The Trade Desk. Even if it doesn't happen anytime soon, this stock could easily double again over the next two years.

3. Valens GroWorks

Valens GroWorks, which recently rebranded itself as The Valens Company, is by far the smallest of these three stocks, with its market cap below $300 million even after more than doubling in 2019. But if you're looking for a great way to profit from the cannabis boom, Valens could be it.

The company provides cannabis extraction products and services used in producing cannabis derivative products. Its customers currently include major Canadian cannabis producers such as Canopy Growth, HEXO, Organigram, and Tilray.

Valens is in the right place at the right time. The Canadian cannabis derivatives market, dubbed "Cannabis 2.0," is just cranking up. Cannabis extracts, edibles, and non-edible derivatives could generate sales of close to 6 billion in Canadian dollars by 2025, according to projections from Ernst & Young.

There are other cannabis extraction services providers. However, Valens offers five extraction techniques -- more than any other company in the industry -- and is the only extraction provider to offer third-party lab testing. I think that Valens will be able to continue differentiating itself and view it as one of the top marijuana stocks on the market right now.