A little more than a year after the stock market notched its fastest recovery ever from a bear market low, investors are getting nervous about owning equities. Interest rates are rising, politicians are playing chicken with the debt ceiling, and the high-flying tech stocks that have powered a 113% run since the March 2020 lows are showing weakness.

That's why I think West Pharmaceuticals (WST -0.83%), ResMed (RMD -0.18%), and Novo Nordisk (NVO -1.20%) are three great companies to consider buying for the long term. They are likely to continue performing well no matter what the stock market does. Here's why.

A caregiver helps a patient take a sample to check their blood sugar level.

Image source: Getty Images.

1. West Pharmaceutical Services

One of the least-reported stories of the pandemic has been the astronomical amount of supplies required to vaccinate people around the globe. Syringes, seals, and stoppers needed to be rapidly made and put to use to curb the pandemic. West is a leader in creating these delivery systems for injectable drugs. It designs and manufactures its own components, as well as those of others. 

The company is well-diversified across geographies, products, and customer type. About half of its business is done in the Americas region, and three-quarters of sales are its proprietary products. Of those, biologics and pharmaceuticals lead the way, with products for generic drug makers accounting for the rest. As you might imagine, business is booming.

After posting annual revenue growth in the mid-single digits for the last decade, sales for the first half of this year came in 37% higher than the same period last year. Net income was up 104%. It has repeatedly raised full-year guidance and now expects sales of $2.77 billion -- 29% above 2020.

Management knows how to convert those extra sales into profits. Operating margins have risen consistently over the past decade. It's why earnings-per-share growth has outpaced revenue growth nearly 6-to-1 during that span.

Chart showing rise in West's TTM revenue and EPS since 2012.

WST Revenue (TTM) data by YCharts

West Pharmaceuticals is a company selling critical components to an industry that is perpetually improving our quality of life. With a management team that knows how to squeeze profits out of incremental sales, I think it's a stock investors can feel comfortable buying and holding for a decade or more.

2. ResMed

If you were asked to name a market leader with 15 million cloud-connectable medical devices, you could be forgiven for not naming ResMed. The purveyor of devices and masks for sleep apnea, chronic obstructive pulmonary disease (COPD), and other respiratory ailments only gets about 12% of its revenue from software-as-a-service (SaaS). However, the data from those devices is helping drive innovation that improves both outcomes and experience for patients. 

Like many companies, the pandemic created some one-time effects for the business. In ResMed's case, it was a benefit and a drag. Although many sleep clinics closed for a time, the company tripled its output of ventilators last year to help treat patients with severe COVID-19. It all added up to $3.2 billion in revenue for the fiscal year ending with June 2021 -- up 8% from the previous year. Operating income climbed 12%. Both numbers were well short of its performance in the two years preceding the pandemic.

I expect its performance to rebound as things get back to normal. In fact, ResMed may do much better than its history would suggest. Its primary competitor -- Koninklijke Philips N.V (NYSE:PHG) -- saw the U.S. Food and Drug Administration (FDA) recall many of its respiratory care devices.

CEO Mick Farrell said in the most recent earnings call that demand for its machines has surged dramatically since the action. Unfortunately, supply chain and component constraints are limiting how much benefit the company will realize in the short term. Management expects additional product will flow in the March and June quarters of 2022. 

Investors might have to wait until next year for that bump to materialize, but the company has an incredible runway for growth globally over the long term. Management estimates there are 1.6 billion undiagnosed people in the world who could benefit from its devices, and it is targeting 250 million lives to improve with out-of-hospital care by 2025. That should give shareholders comfort that any gyrations in the market are noise compared to ResMed's overall opportunity.

3. Novo Nordisk

The World Health Organization estimates that the number of people with diabetes has increased from 108 million in 1980 to 422 million in 2014. Some estimate the number at 463 million today. Projections show the number will keep rising. For many, that means taking insulin -- a hormone that helps the body transport sugar from food in the stomach to cells. Novo Nordisk is one of three drug makers that, combined, control 90% of the insulin market. The others are Eli Lilly (LLY -0.62%) and Sanofi (SNY -1.26%)

Despite the dominance, the company has continued to innovate. Although total insulin segment sales were down in the first half of this year compared to 2020, its latest drugs have done well. Rybelsus -- a pill patients take orally each day that mimics a hormone released after a meal -- saw revenue climb 187%. Sales of Ozempic -- which helps the body lower blood sugar -- rose 47%. 

Insulin is an important part of Novo Nordisk's business -- still about 42% of revenues -- but it isn't all of it. Year-over-year sales in the obesity care segment climbed 23% for the first half of 2021. That will be bolstered by the FDA's June approval of Wegovy. It's the company's once-a-week injection that suppresses appetite and slows the emptying of the stomach.

If you are looking for a company that offers stability, Novo Nordisk certainly has it. The company is one of the only makers of a drug that keeps millions of people alive with regular dosing. It's led to revenues nearly doubling over the past decade, earnings per share more than tripling, and dividends that have quadrupled. In a market that looks jittery, it might be time to add one of the most dependable companies in the world to your portfolio.