Axsome Therapeutics (AXSM -1.05%) has been making headlines for two reasons this year. First, the stock has defied the bear market. It has climbed 21% so far this year, while the S&P 500 index has dropped 20%. And second, the company is starting to sell its very first products.

If you invested at the start of this year, you're winning on that investment. But what if you bought shares of Axsome earlier in this company's story? Let's find out how much you would have today if you invested $5,000 in Axsome about three and a half years ago.

Gaining as much as 3,000%

Back in January of 2019, Axsome was trading for about $8 a share. If you invested $5,000 at that time, you would have purchased 625 shares. The stock climbed as much as 3,000% in just a year. Right now, it's settled at about 1,500% higher than it was in early 2019. So today your investment would be worth $28,750.

That's reason to smile. But you might argue your returns would have been even better if you sold at the high point. That's true. You might have more to gain, though, by sticking with Axsome for the long term. Here's why.

As mentioned above, Axsome's story as a commercial-stage company has just started. Back in May, it began selling Sunosi. It acquired this sleep-disorders drug from Jazz Pharmaceuticals. Last year, Sunosi's net product sales rose 104% when it still was part of Jazz's portfolio. In the first six weeks of sales for Axsome, Sunosi brought in $8.8 million. So it looks like Axsome is off to a good start with this product.

But the biggest news: The Food and Drug Administration (FDA) recently approved Auvelity, Axsome's treatment for major depressive disorder. This is a crowded market. But Auvelity offers an important advantage. The drug produces statistically significant improvement in symptoms after only one week of treatment. Rival products take several weeks to produce results. 

A potential blockbuster

This advantage could push Auvelity into blockbuster territory. The drug might reach $1.3 billion in sales by 2029, according to GlobalData. It also could win over patients since it isn't associated with weight gain, a common side effect of antidepressants.

Axsome will begin selling Auvelity this year. So by the end of the year, two products will drive growth at the company. But there may be others in the not-too-distant future.

The company stumbled when the FDA rejected its migraine candidate. But after a recent meeting with the agency, Axsome is set to resubmit it in the third quarter of next year. There's reason to be optimistic. The FDA's questions had to do with chemistry, manufacturing, and controls. These issues are much easier to resolve than a problem with efficacy, for example.

And the rest of Axsome's pipeline includes four candidates that are in phase 2 or phase 3 development. If all goes smoothly, it could launch additional products in just a few years. And this should equal significant earnings growth.

What does this mean for investors? If you've already bought shares, you were right to hold on to them. Axsome is just getting started when it comes to revenue. If you haven't yet purchased the shares, it's not too late. The stock has come down from highs reached before it even had products on the market. Over time, it could make its way back to those levels -- and possibly higher.

So, yes, if you bought Axsome back in 2019, you're winning on the investment. But if you hang on, you might have even more to gain.