Here's a fact: You don't need huge sums of money to start (or continue) investing. Any amount, if placed wisely, could eventually bring you great returns. Today, let's consider $500. With that amount you could buy one of the following growth stocks -- or invest in all three. They could double your money over time.

So, what stocks are we talking about? Teladoc Health (TDOC -1.04%) is a leader in the growing market of telemedicine. Moderna (MRNA -8.05%) is on its way to becoming more than a coronavirus vaccine stock. And Axsome Therapeutics (AXSM 2.09%) is starting what may become a billion-dollar revenue story. Let's find out more.

1. Teladoc Health

Teladoc shares have dropped 67% this year. Investors worried after the telemedicine company reported two, billion-dollar non-cash goodwill impairment charges. These were linked to Teladoc's purchase of Livongo, a specialist in chronic care, in 2020. That added to earlier concerns about the company's lack of profitability so far.

But there's reason to be optimistic about Teladoc over the long term. And that's showing in its recent share performance. The stock has climbed 21% over the past month.

In the third quarter, Teladoc's net loss narrowed. The company's revenue and visits continue to climb in the double-digit-percentage range. And over time, Teladoc has won over big business; it serves more than half of Fortune 500 companies.

Yet there still is plenty of room for growth. For example, 92 million people in the U.S. have access to a Teladoc product. That's out of a total of 298 million U.S. insured lives. At the same time, the telemedicine market is forecast to grow by double digits. Teladoc is likely to benefit.

As for valuation, Teladoc is a bargain right now. It's trading for 2 times sales, nearly its cheapest price ever.

2. Moderna

Moderna has been generating billions of dollars in revenue and profit since it began selling its coronavirus vaccine. And that initially boosted the shares. This year, though, worries about Moderna's revenue in a post-pandemic world weighed on the stock. It's down 28% so far in 2022. But, like Teladoc, the shares have rebounded over the past month.

We're now beginning to see what Moderna will look like once the pandemic is over. The company has offered estimates of market size for its coronavirus booster. Yes, revenue probably will come down from today's level. But an annual booster still may be a source of significant, and recurrent, revenue for Moderna.

Let's add to that the progress Moderna is making on other non-coronavirus programs. Three are in phase 3 trials. And Moderna says two of those may result in product launches in the coming two to three years. It's also important to note that these two candidates -- vaccines for flu and respiratory syncytial virus -- could bring in blockbuster revenue.

All of this together means Moderna has a bright future ahead -- with potentially a steady stream of billion-dollar revenue. So Moderna's share performance may be just getting started.

3. Axsome Therapeutics

Axsome shares have outperformed the general market this year. That's on optimism about its first commercialized drugs. But shares could climb a lot higher over time as revenue grows.

And the revenue story starts now. The company acquired sleep disorder drug Sunosi from Jazz Pharmaceuticals earlier this year. The third quarter was its first full quarter of sales as an Axsome product. It brought in more than $16 million -- and prescriptions climbed 15% year over year.

Axsome just launched its antidepressant Auvelity in recent weeks. The drug could stand out because it's fast-acting -- showing results after only one week. Auvelity could reach $1.3 billion in sales by 2029, according to GlobalData. So this could be a major product for Axsome.

Meanwhile, Axsome's pipeline candidates are mainly late-stage. This is positive because, if all goes well in clinical trials, Axsome could launch additional products in the next few years. The next one may be a candidate for migraines. The company plans to submit it for regulatory approval next year.

Right now, Axsome isn't profitable. And expenses will increase as it ramps up infrastructure to sell its current products and advance the pipeline. But there's plenty of potential for sales growth in the near term and beyond. This, and pipeline progression, could drive the shares significantly higher from here.