Growth stocks are back in style after getting battered in last year's downturn. Some, though, never went out of fashion in the first place. That's the case with this trio of biotech stocks: Vertex Pharmaceuticals (VRTX 1.53%), Eli Lilly (LLY 2.03%), and Novo Nordisk (NVO -0.21%). All three have put up solid performances over the past year. These growth stocks may be just getting started, however. Let's find out why all three are worth investing in today. 

1. Vertex Pharmaceuticals

Vertex Pharmaceuticals has a significant catalyst ahead. The company is awaiting approval for exa-cel, a treatment for sickle cell disease (SCD) and beta-thalassemia (TDT) developed with CRISPR Therapeutics. Vertex is already growing its top line faster than most biotechs, especially those of its size. In the second quarter, the company's revenue of $2.49 billion jumped by 14% year over year.

The addition of exa-cel to the biotech's portfolio could substantially improve its financial results, especially considering the vast addressable market it is targeting with this gene-editing treatment. Given an initial population of 32,000 patients in SCD and TDT Vertex and CRISPR Therapeutics will seek to treat -- and considering gene-editing therapies command prices well above $1 million -- exa-cel could be looking at an opportunity worth tens of billions of dollars.

Of course, Vertex will continue to rely on its cystic fibrosis (CF) franchise that has made it so successful. It is working on new CF therapies to address the remaining patients who aren't eligible for its current treatments. Vertex is also developing medicines in other areas and plans to launch five products in the next five years. For instance, its potential treatment for acute and neuropathic pain is progressing steadily.

Vertex Pharmaceuticals' early stage programs, such as those that target type 1 diabetes, could also lead to blockbusters down the road. Vertex's lineup is already solid, but considering the potential for new products its pipeline could deliver in the short and mid term, the biotech's shares look like a screaming buy

2. Eli Lilly

Eli Lilly also showed impressive top-line growth for a biotech giant in the second quarter. Total revenue came in at $8.3 billion, 28% higher than the year-ago period. The company's indisputable key asset has become Mounjaro, a diabetes treatment that has been on the market for a little over a year and is already generating almost $1 billion in sales per quarter.

That's an impressive feat; some medicines have been on the market for years and still don't generate $1 billion annually. And Mounjaro won't likely stop growing anytime soon. Investors should expect plenty of label expansions for the medicine -- first up, in helping with weight loss for diabetes patients. Health authorities are currently considering Mounjaro for this potential label expansion. There will be many more in the future.

Eli Lilly's lineup has other important growth drivers, from cancer medicine Verzenio to immunosuppressant Taltz. Elsewhere, the company is also inching closer to launching new important products, most notably Alzheimer's disease treatment donanemab. The AD market could get more competitive because plenty of drugmakers are targeting this area, but Eli Lilly should succeed considering donanemab produced solid results in a phase 3 trial, and there aren't that many novel AD therapies on the market yet.

Donanemab could earn approval in the U.S. within the next year, thereby strengthening Eli Lilly's already solid portfolio. With all that going on, the biotech isn't done beating the market -- far from it. 

3. Novo Nordisk

Novo Nordisk is a diabetes specialist. It boasts several medicines in this area (or in obesity care) that are growing their sales rapidly. These include Wegovy, Saxenda, Ozempic, and Rybelsus. Fueled mainly by these products, Novo Nordisk's total sales in the first half of the year were 107.7 billion Danish kroner ($15.7 billion), up 29% versus the year-ago period. The company also maintained its lead in the diabetes care market, with a 32.7% share as of May, 1.7% higher than the comparable period of the previous fiscal year.

Novo Nordisk's dominance in this niche, despite competition from companies like Eli Lilly, is impressive. It should help the company maintain its recent momentum, especially as it adds new products to its portfolio. The company's pipeline currently features about a half-dozen diabetes or weight-loss products in the late stage or registration stage.

One of them is icodec, a once-weekly insulin option. Both Eli Lilly and Novo Nordisk are racing to develop an insulin product that can be administered once a week, and with good reason; diabetes patients typically have to take insulin daily. This would greatly simplify their lives. Novo Nordisk is also looking to diversify its portfolio with programs in various therapeutic areas such as rare diseases, neurology, and more.

So it's not too late to buy shares of Novo Nordisk, as the biotech still has a bright future ahead of it.