While investors in or nearing retirement may prioritize income or security over chasing the highest returns possible, many portfolios could benefit from owning a growth stock or two. However, some of the best growth companies are the ones you've never heard about. 

For instance, Tandem Diabetes Care (NASDAQ:TNDM) develops and distributes user-friendly glucose monitoring devices for individuals with type 1 and type 2 diabetes. That's not exactly the most obvious growth opportunity, but faster-than-expected adoption has the business expecting to grow revenue 94% compared to 2018.

Meanwhile, Catalent (NYSE:CTLT) and its predecessor have been manufacturing softgel drug delivery capsules since the 1930s. The business has since expanded into other drug delivery technologies and is poised to start growing at its fastest pace in recent memory thanks to a recent acquisition in gene therapy manufacturing.

Here's why these two growth stocks should be on the radars of healthcare investors.

A stethoscope, notepad, drug capsules, and a laptop.

Image source: Getty Images.

This stock is cooling off, but growth remains red hot

Shares of Tandem Diabetes Care have gone sideways since March 2019, but investors shouldn't take that as a sign of flatlining operating results. The business is on pace to achieve quarterly operating profits in the second half of 2019, and quarterly net profits in 2020. 

The path to profits has been shortened by solid growth: After previously expecting at least $300 million in full-year 2019 revenue, management now expects at least $350 million on the year. That would represent year-over-year growth of 94%. The growth trajectory may slow in relative terms as revenue totals grow larger, but the business sees a significant growth opportunity ahead.

There are currently 1.6 million Americans with type 1 diabetes who are also candidates for pump therapy. However, only about 550,000 individuals used insulin pumps in September 2018, or about 28% of eligible patients, when the company's t:slim X2 insulin pump launched. Tandem Diabetes Care wants to increase that figure to 50% with its user-friendly, software-driven device. Considering the business sold 21,258 devices in the second quarter of 2019, it appears to be executing on its vision.

What's more, there's ample room to expand outside of the U.S. International sales are expected to comprise at least 15.7% of total revenue in 2019, compared to 5.3% in 2018.

Tandem Diabetes Care also has considerable potential in its product pipeline. The company is awaiting regulatory approval for the t:slim X2 with Control-IQ technology, a next-generation algorithm (current devices use the Basal-IQ algorithm) that would allow for enhanced predictive and real-time glucose monitoring. The new offering could launch before the end of 2019, and catalyze growth in the year ahead. Researchers are also developing the t:sport, a next-generation hardware platform that's smaller and more powerful. 

Simply put, shares have gone sideways in recent months to allow the business to earn its premium valuation of $3.5 billion. While the stock remains relatively expensive at 10 times expected 2019 sales, there aren't many places to find (soon-to-be) profitable growth quite like what Tandem Diabetes Care offers.

A model of DNA in the foreground and a teacher in the background.

Image source: Getty Images.

Can gene therapy ignite growth?

Catalent isn't exactly known for being a growth stock, but that could be about to change. To be fair, the business has performed well in recent years. Revenue has grown 36% from fiscal 2016 to fiscal 2019 (the period ending June 30). Shares have delivered a 90% gain in that span, compared to a return of 65% for the S&P 500 including dividends. 

Despite the progress and market-beating returns, the drug delivery specialist has left investors wanting more. The business has been working hard to offset falling revenue from core operating segments with growth from the best opportunities available: biologic drugs. The difficulty and rare expertise needed to competently manufacture biologic drugs creates higher margin revenue for companies able to cash in, and Catalent can be counted among the lucky few.

The business leaned on its biologics and specialty drug delivery segment for the majority of revenue and EBITDA growth in fiscal 2019, but investors should expect a step-change in the year ahead. That's because Catalent closed the $1.2 billion acquisition of gene therapy manufacturing leader Paragon Bioservices in late May. It contributed for less than half of fiscal Q4 2019, and was on pace to deliver at least $200 million in revenue in calendar 2019. That alone is equivalent to 8% of Catalent's fiscal full-year 2019 revenue. And that was before a slew of new partnerships and supply agreements were announced.

Investors should expect management to make the most of the opportunity by making sizable investments in the new business, now called Paragon Gene Therapy, for the foreseeable future. That includes new manufacturing assets to drive value for AveXis (the leading gene therapy developer, now a subsidiary of Novartis), NovaVax, Amicus Therapeutics, and the like. Of course, that could weigh on margins in the short term, with the expectation for greater growth in the long run.

Considering the business delivered the highest operating earnings in fiscal 2019 in at least the last decade, Catalent is well-positioned to capitalize on the growth opportunity and its new leadership position in gene therapy manufacturing. Investors with a long-term mindset shouldn't overlook the significance.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.