The past 15 months haven't been easy for growth stock investors. The Nasdaq Composite index has fallen a disappointing 25% since the beginning of 2022, making this an unusually long bear market.

You don't need an economics degree to see that every bear market in history has been wiped away by subsequent recoveries. We don't know when the next recovery period will begin, but buying top growth stocks now, while their prices are depressed, gives you a better-than-average chance to realize market-beating gains down the road.

Over the past year, Vertex Pharmaceuticals (VRTX 1.25%) climbed 23%, while the Nasdaq Composite tumbled 15% lower. Shares of the medical technology company DexCom (DXCM 1.89%) soared 42% over the past six months. Read on to see why these two could shoot even higher during the next bull rally.

1. Vertex Pharmaceuticals

Cystic fibrosis is a progressive and ultimately fatal disease that affects around 83,000 people globally. Vertex Pharmaceuticals is the only company on the planet marketing treatments that address the root cause of the disease: defective copies of CFTR protein.

Without functional copies of CFTR on the surface of cells that line lung tissue, cystic fibrosis patients produce sticky mucus that makes it hard to breathe. Dozens of known mutations can disrupt CFTR, but treatment with Trikafta can improve lung function for around 90% of patients.  

We'll soon know if Vertex can treat patients who don't respond to Trikafta. The company recently began its first clinical trial with VX-522, an inhaled treatment under development in collaboration with Moderna. Once inhaled, this messenger RNA-based drug should lead to the production of functional CFTR where it's needed most.

Cystic fibrosis drug sales soared 18% last year to reach $8.9 billion. Despite plowing $2.5 billion into research and development, earnings soared 42% year over year.

Heavy investment in the development of drugs beyond a single rare disease could allow Vertex to grow by leaps and bounds in the years to come. The company is swinging for the fences with VX-264, a cell therapy designed to replace insulin-producing pancreatic islet cells for patients with type 1 diabetes.

Right now, you can buy shares of Vertex for just 23.8 times trailing earnings. That's a reasonable price to pay for a stock growing earnings at a fraction of this company's pace. With a development pipeline full of potential blockbusters, buying the stock now gives you a great chance to come out way ahead over the long run.

2. DexCom

DexCom is a medical device company that markets constant blood glucose monitors (CGMs). As such, it has a big potential customer base. Roughly 11.3% of the U.S. population has diabetes, and around 38% of adults have prediabetes.

DexCom's latest CGM, the G7, earned FDA clearance late last year and launched this February. The G7 is just a little bigger than a competing device from Abbott Laboratories, and it could gain a large share of the lucrative CGM market.

DexCom expects total revenue to rise between 15% and 20% in 2023.

Don't be surprised if DexCom blows past its sales estimate by the end of the year. An updated policy from the Centers for Medicare and Medicaid Services (CMS) could double the market for CGM devices by making less-severe patients who don't receive intensive insulin injections eligible for reimbursement as well.

DexCom's leading position in the lucrative CGM space makes it a good stock to buy and hold over the long run. That said, cautious investors might want to wait for a pullback. The stock is trading at a nosebleed-inducing multiple of more than 100 times forward-looking earnings expectations.