Things simply couldn't be better for growth stocks right now. The Federal Reserve has pledged to keep interest rates at or near historic lows through at least 2023, and it's supporting this low-rate environment by purchasing Treasury bonds each month to drive down long-term yields.

Meanwhile, the Biden administration appears intent on passing as much fiscal stimulus as is needed to right a struggling economy. Access to abundant cheap capital is usually a recipe for growth stock outperformance.

But not all growth stocks are created equally. If you're looking to add no-brainer growth stocks to your portfolio at an opportunistic price, the following three are begging to be bought.

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AstraZeneca

For roughly two decades, big pharma AstraZeneca (NASDAQ:AZN) was anything but a growth stock. Like most pharmaceutical stocks, AstraZeneca was basking in the cash flow generated by a handful of blockbuster therapies. However, it was also clobbered by the loss of patent exclusivity with these key names. Replacing lost revenue doesn't happen overnight, and for years it made AstraZeneca an easily overlooked company.

But that was the past. Nowadays, AstraZeneca is a bona fide growth stock that I suspect offers steady and sustainable upside for many years to come.

The biggest organic growth driver for the company is its oncology portfolio, which includes blockbusters Tagrisso, Imfinzi, and Lynparza. Through the first nine months of 2020, oncology product sales grew by 24% on a constant-currency basis to almost $8.2 billion, accounting for close to 43% of total company sales. With improved cancer-screening diagnostics, demand for oncology products and duration of use tend to increase over time. Since cancer patients don't get to choose when they get sick, demand for AstraZeneca's leading oncology products remains steady in any economic environment. 

AstraZeneca is also making waves on the acquisition front. In mid-December, it agreed to buy one of my favorite biotech stocks, Alexion Pharmaceuticals (NASDAQ:ALXN), for $39 billion in a cash-and-stock deal.

Alexion is special for two reasons. First, it caters to ultra-rare "orphan" diseases. By focusing on treatments for small patient pools, Alexion often avoids direct competition, and it rarely faces any pushback from health insurers on pricing.

The other important factor with Alexion is that it developed Ultomiris as a replacement therapy for its blockbuster drug Soliris. There were concerns that generic or biosimilar drug developers would go after Soliris' indications upon expiration of its exclusivity. However, with Ultomiris offering far fewer annual administrations than Soliris, its approval by the Food and Drug Administration effectively secured Alexion's core cash flow for another decade, if not longer.

On the heels of low double-digit sales and profit growth, AstraZeneca is begging to be bought.

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Facebook

Although I'll get no points for innovation from the judges, social media kingpin Facebook (NASDAQ:FB) has all the attributes of a growth stock you're going to want to add now.

To address the 800-pound gorilla in the room: even Facebook faces growth hurdles. In the company's most recent quarterly report, it noted that a shift in advertising preferences in Apple's iOS 14 could disrupt some of its ad-targeting potential. Facebook has also been criticized by select Democrats on Capitol Hill who believe the company has too much power in the social media space. And yet, even facing these challenges, Facebook is a hands-down, no-brainer buy.

Facebook's dominance is on display any time the company lifts the hood on its quarterly operating performance. As of the end of 2020, the company's namesake site brought in 2.8 billion monthly active users. If you include its other owned assets (Instagram and WhatsApp), this figure jumps to 3.3 billion family monthly active users. There's simply not another social media platform that can offer advertisers such a broad audience. It's worth noting that, even during the worst economic downturn in decades, Facebook grew its advertising revenue by 21% last year. 

The other important catalyst that I cannot stress enough about Facebook is that it still hasn't monetized all its available assets. Its $84.2 billion in ad revenue generated in 2020 almost exclusively came from Facebook and Instagram. The company has yet to really open the floodgates on Facebook Messenger or WhatsApp. These represent four of the six most-visited social platforms on the web. Once Facebook begins monetizing all of its assets, its sales, profits, and cash flow are going to leap higher.

What makes Facebook so incredibly attractive is its valuation relative to its cash flow. Wall Street's consensus is for $19.49 cash flow per share by 2023. That works out to a current multiple of 13.8 times cash flow (in 2023). By comparison, Facebook has averaged a cash flow multiple of more than 22 over the past five years. It may not look like a bargain on the surface, but Facebook is begging to be bought at these levels.

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Amazon

Would you believe me if I told you that Amazon (NASDAQ:AMZN), the third-largest publicly traded company in the U.S., is a screaming bargain, if not an outright value stock? My guess is probably not.

For more than two decades, Amazon CEO Jeff Bezos has valued growing the company's market share at the expense of near-term profits. This has led Amazon to regularly be valued at triple-digit forward price-to-earnings ratios. But as you'll see, even at these triple-digit P/Es, Amazon is begging to be bought by growth-seeking investors.

Just as Facebook is the Goliath of the social media space, Amazon is the dominant force in U.S. e-commerce. Having reviewed retail reports and Wall Street data, most estimates settle on the company controlling between 39% and 44% of all U.S. online sales. At minimum, that's 30 percentage points higher than its next-closest competitor.

Even though retail margins tend to be nothing special, Amazon is able to make the most of its dominance. The company has enrolled more than 150 million people around the globe in its Prime membership program. The fees Amazon collects from Prime help cushion its narrow retail margins and ensure that it can undercut brick-and-mortar retailers on price. Also, paying members are more likely to stay within Amazon's ecosystem of content, products, and services.

The Amazon growth story is very much about cloud infrastructure services, too. Amazon Web Services (AWS) grew sales by 30% last year, with the $12.7 billion in fourth-quarter sales equating to an annual run-rate of $51 billion. Since cloud margins are many, many times higher than retail margins, a rapidly growing AWS could potentially triple Amazon's operating cash flow by 2023 or 2024

After ending every year of the 2010s with a price-to-cash-flow multiple of 23 to 37, Amazon's cash flow multiple of 14 for 2023 makes it one heck of a value.

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.