Biotech stocks are a great way to grow your portfolio over time -- you can get in early on an innovator and benefit as it brings exciting candidates through the pipeline to commercialization. Of course, the drug development path isn't always smooth, so as an investor, you have to be comfortable with some risk. But if you are, these types of stocks can truly pay off years down the road.

So which players make a great buy today with the potential for a win tomorrow? I'll vote for Crispr Therapeutics (CRSP 9.42%) and Axsome Therapeutics (AXSM -0.21%). These companies are at the very start of their product commercialization story -- and opportunity for growth lies ahead. Let's find out more.

1. Crispr Therapeutics

Crispr is a specialist in gene editing, or the repair of faulty genes responsible for disease. The company has reached an exciting moment, with the possibility of its first product launch just months away. Crispr and partner Vertex Pharmaceuticals expect a regulatory decision on exa-cel for sickle cell disease in December and a decision on the potential treatment for beta thalassemia in March.

Today, treatment options for these blood disorders are limited, so exa-cel, designed as a one-time curative treatment, could be popular among doctors and patients. The product is even expected to reach blockbuster status.

This is positive for Crispr for two reasons. First, a commercialized product will bring in revenue and the possibility for earnings growth. Second, a regulatory nod could be seen as a vote of confidence in Crispr gene-editing technology, used throughout its pipeline.

Speaking of pipeline, Crispr has another product that's approaching the finish line. Immuno-oncology candidate CTX-110 is involved in a phase 2 trial that could support a regulatory submission. If all goes well, Crispr could have more than one product on the market within the next few years.

Now, let's take a look at Crispr's share price. It's trading at a much lower level than it was a couple of years ago -- when we had a lot less visibility regarding the safety and efficacy of its candidates. A potential exa-cel approval and approvals of other candidates down the road could clearly push the shares higher over time.

2. Axsome Therapeutics

Last year, Axsome won its first product approval, for antidepressant Auvelity, just months after it started selling sleep disorder drug Sunosi -- a product it acquired from Jazz Pharmaceuticals.

In the second quarter, Auvelity sales climbed 76% from the previous quarter, and due to the successful launch, the company is increasing its Auvelity sales force. Auvelity stands out from others on the market because it's fast-acting, reducing symptoms after just a week.

Auvelity and Sunosi both have seen increases in prescriptions from quarter to quarter, and the company predicts U.S. peak sales of as much as $3 billion for Auvelity and $500 million for Sunosi. Axsome also has a full pipeline of late-stage candidates that, together with Auvelity and Sunosi, could generate U.S. peak sales of more than $11 billion. It expects to launch most of these potential products by 2025.

Axsome specializes in disorders of the central nervous system, and its candidates span areas such as Alzheimer's disease agitation, smoking cessation, and migraines.

Now, let's look at valuation. Axsome shares are trading for 19 times sales, down from more than 24 last year. This looks dirt cheap, considering the potential products that could launch in the very near future.

Of course, candidate failure can happen any time -- even during regulatory review -- but the fact that Axsome's pipeline is late stage means some risk is reduced. That's because the candidates have made it past many safety and efficacy hurdles.

All of this means Axsome is a no-brainer biotech stock to buy now and hold on to for the long term.