With the Nasdaq Composite still firmly entrenched in bear market territory, if you're feeling discouraged about the state of your portfolio and the performance of some of your favorite stocks, you're certainly not alone. However, even in volatile markets, compelling buying opportunities remain for forward-thinking, patient investors.

That said, in this type of environment, it's even more important than usual to differentiate between businesses that have clear paths to growth and are simply trading down amid tough macro conditions, and those that are seeing their shares decline for valid reasons that suggest they'll face long-term headwinds.

Two stocks that in my view belong firmly in the former category are DexCom (DXCM 0.13%) and Procter & Gamble (PG -0.66%).

1. DexCom 

If you're searching for a non-cyclical company with products that are consistently in demand, regardless of the macro environment or consumer sentiment, DexCom could be a no-brainer contender for your portfolio. It's a leading developer and manufacturer of continuous glucose monitoring (CGM) devices in the world. Its devices are worn by millions of Type 1 and Type 2 diabetics globally.

With a global market share of roughly 50% in the CGM space, it's fair to say that DexCom has considerable room to grow even in a tough economic environment. The company is currently in the process of launching the latest generation of its flagship CGM device, the G7. The G7 system is much smaller and lighter than its predecessor, and has the fastest warm-up time of the CGM devices on the market. 

In the third quarter, DexCom delivered year-over-year revenue growth of 18% to $770 million while its bottom line grew by 16% to $101 million. Over the past decade, its annual revenue have grown by more than 2,400%, while the stock has delivered an astonishing total return of 3,300%.

CGMs are not discretionary products. These devices can make a life-or-death difference in the health of their users. It's also worth noting that a growing number of private insurers have expanded their coverage to include CGM devices, and Medicare and Medicaid last year adjusted their rules in ways that expanded their coverage for those devices.

As such, DexCom's total addressable market continues to expand, and demand for its products should continue to grow. In fact, the American Diabetes Association estimates that 1.4 million Americans are diagnosed with diabetes annually.  

At its current share price, a $1,000 investment in DexCom would add about nine shares to your portfolio. 

2. Procter & Gamble

Speaking of non-cyclical businesses, Procter & Gamble is another compelling stock for long-term investors to consider, and one that is a Dividend King to boot. At its current share price, its payout yields 2.5% for investors, and it has raised its dividend annually for 66 straight years. 

Over the past decade alone, management has boosted the dividend by more than 60%, helping the stock to deliver a total return of 188% for investors. Not bad for a consumer staples stock that might get a bad rap among some investors for being a "boring" business. Often, it's those-value oriented businesses, even the ones that can be considered boring, that can deliver the most sustainable returns in a wide variety of environments.

Procter & Gamble's products span a wide range of consumer needs, from personal care products to oral health to hair care to home care. Household names like Pampers, Downy, Tide, Bounty, Charmin, Always, Tampax, Gillette, Herbal Essences, Pantene, and Old Spice are all part of its family of brands. 

In the most recently reported quarter, Procter & Gamble grew its organic sales by percentages in the mid-to-upper single digits across each of its five core business segments. Overall, organic sales (which exclude the impacts of currency exchange fluctuations) rose 7% from the prior-year period. Even with foreign currency headwinds factored in, total net sales still rose 1% year over year to $21 billion. The company also reported net earnings of about $4 billion for the quarter. And over the past five years, Procter & Gamble has grown its top and bottom lines by 20% and 51%, respectively.  

A $1,000 investment in Procter & Gamble at its current share price would add approximately seven shares to your portfolio.