It's not always easy to be a long-term investor, particularly when contending with the natural cyclicality that the stock market presents if you buy and hold through bull as well as bear markets.

Investing consistently during all types of market environments is key. So is maintaining your positions in quality companies unless and until your investment thesis regarding them no longer applies, or you feel that they have exhausted their value proposition for your portfolio.

If you're looking for unstoppable growth stocks to buy and hold for at least three to five years, and you have $1,000 to add to your portfolio right now, here are two names you should consider.

1. DexCom

Medical device company DexCom (DXCM -0.41%) specializes in the diabetes care space. Its continuous glucose monitoring (CGM) devices are used by diabetes patients around the world to track their blood sugar levels and manage potential adverse events.

Shares of DexCom have plummeted in recent months, and are now down by about 40% year to date. Though the company is still in solid financial shape, its revenue growth has slowed over the last few quarters.

This happened for a few reasons, most of which appear to be short term in nature. For example, an unexpected spike in the number of patients using rebates for its flagship G7 CGM has resulted in rebate eligibility over a schedule that was three times faster than the company experienced with its predecessor device, the G6 CGM.

Other factors such as restructuring of its sales teams amid shifts in its product lineup, and lower-than-usual performance in its durable medical equipment (DME) channel have also impacted revenue. Management broadly expects these complications to subside in the coming quarters, and it's actively working to expand its DME partnerships with distributors.

Some portion of the stock's decline is also a reflection of investors' expectations that the widening use of GLP-1 drugs in diabetes care may reduce the long-term utility of CGM devices. However, therapeutic options like GLP-1 drugs do not replace the need for a CGM, and these devices continue to provide a range of use cases for the diabetic population as well as pre-diabetic individuals.

In the third quarter, DexCom's U.S. revenue declined by 2%, while international revenue rose 12%. Overall revenue was $994 million, up 2% year over year. Management has said that rebate eligibility likely peaked in Q3, so that impact to its top line should not be surprising.

Bear in mind, DexCom is still very profitable. Net income for the quarter totaled $134.6 million, which was a healthy 12% increase from the year-ago period. DexCom finished the quarter with $2.5 billion in cash and cash equivalents on hand, and it brought in about $535 million in free cash flow over the trailing 12-month period.

DexCom also just launched Stelo, a new biosensor for adults with prediabetes and type 2 diabetes who are not on insulin. It's the first over-the-counter glucose biosensor in the U.S. In sum, this is not the tale of a dying business, and investors who are in it for the long haul could find this a wise time to buy shares on the dip.

2. Revolve Group

Revolve Group (RVLV 1.57%), too, has had to contend with difficult investor sentiment. While shares of the e-commerce fashion company are actually up about 100% from the start of 2024 at the time of this writing, the stock is still down by about 170% from the all-time high it reached in November 2021.

The recent consumer spending environment has been tough on many online retailers, and this has impacted Revolve's financial growth. However, the company, which targets everything from affordable to premier luxury, has stayed the course, relying on the power of its long-standing marketing partnerships with influencers, artificial intelligence solutions that underpin its platform, and a diverse range of brands to drive business growth. Sales are still growing steadily, and Revolve Group is also profitable.

As of the end of the third quarter, its trailing 12-month active customer base had grown by 5% year-over-year to 2.6 million individuals. Net sales in Q3 came to $283 million, a solid 10% bump from one year ago. Broken down by segment, the Revolve segment generated sales of $243.4 million, up 12% from one year ago. The company's in-house premier luxury brand, FWRD, had revenue of $39.7 million -- down by less than 0.5% year over year.

More impressive was Revolve Group's net income. Its bottom line was just shy of $11 million for the quarter. That was a 238% increase from the prior-year period, a time when it was also dealing with large one-time costs related to settling a legal matter.

Revolve offers more than 100,000 apparel and footwear products through its e-commerce platform, as well as home products, beauty, and accessories. It sells thousands of brands including 25 owned brands along with many coveted third-party brands. In 2023, around 79% of Revolve Group's net sales across all brands were at full price.

Last year, the company generated $1.1 billion in net sales from more than 2.5 million active customers, with an average order value of $297. As one of the largest fashion e-commerce brands in the U.S., Revolve Group has plenty of opportunities for growth in a fast-growing addressable market. Its underlying finances are strong, and its business is demonstrating resilience even as consumer spending patterns are shifting.

Overall, there appears to be a compelling case for snagging at least a few shares of this top e-commerce stock.