Healthcare stocks can be great long-term buys, and with the coronavirus in the headlines on a daily basis, some are proving to be attractive buys in the short term as well. Gilead Sciences (GILD -0.82%) is an example of a stock that's been flying high in recent weeks on news that its drug remdesivir may be an option to treat the virus. But that alone may not be enough to make the stock a good long-term investment, especially when compared with Amgen (AMGN -0.97%), which may be able to provide investors with a bit more stability and predictability than Gilead. Let's take a closer look at these two stocks to see which is the better long-term investment today.

Does Amgen have enough growth?

Amgen released its full-year results on Jan. 27, and it was an underwhelming performance for the company. The drug manufacturer's revenue of $23.4 billion was slightly down from the prior year, and since 2015, the company's top line has risen by just 7.8%. It's not the kind of growth that's going to inspire a lot of excitement from investors, which explains why over the past five years the stock is up just 36%, well below the S&P 500's returns of over 50%. But that's still better than the 24% decline Gilead's been on during that time.

Amgen's been consistently profitable over the years, but its net income of $7.8 billion in 2019 was also down 6.6% from the prior year. The good news is that it has averaged a profit margin of at least 23% in nine of the past 10 fiscal years. But if sales don't improve, the bottom line won't get any stronger.

People working in a lab. A man at right uses a microscope while others look at computer screens.

Image source: Getty Images.

The one bright spot that can help change that trajectory is the acquisition of Otezla. Amgen acquired the arthritis drug for $13.4 billion from Celgene and the transaction was completed in November, meaning that investors will start to see Amgen's top line get a boost from the new drug in 2020. Otezla generated $1.6 billion in revenue in 2018. Amgen looks to expand Otezla, sell the drug in more markets, and seek approvals for new indications as well.

Is Gilead still a buy if remdesivir fails?

Gilead's struggled with growth, too, but the company is attracting the attention of a lot of investors with its remdesivir drug showing potential to treat the coronavirus. With more than 3,000 deaths from COVID-19 and around 100,000 cases, there's ample demand for a treatment option, especially at a time when not only people but the markets as a whole are jittery about what the long-term impact may be if a solution is not found soon.

The stock's been one of the few on the markets that's done well over the past month because of the possibility that the drug will work effectively. But if the drug manufacturer is unsuccessful in providing patients with a treatment option for the coronavirus, Gilead goes back to being another dividend stock that's struggling to find growth. Although it has more than 100 clinical studies that it's working on, the company is still struggling to make up lost sales from Harvoni. The hepatitis C drug generated more than $9 billion in revenue for Gilead back in 2016, but the company has since transitioned to a lower-priced genetic product to help it stay competitive.

Like Amgen, Gilead's also had no problems staying in the black over the years, but the problem is that in recent quarters there's been much more volatility. Putting aside a third-quarter result that was weighed down by investment-related expenses, Gilead's profit margin has still ranged between 0% and 46% over the previous four quarters. The inconsistency makes it a bit of a risky buy moving forward, as it may be difficult to predict the company's performance in future quarters.

Why Amgen is the better overall buy

Gilead's stock price can take off this year if remdesivir proves to be successful in treating people with the coronavirus. The problem is, that's not a guarantee and it can just as quickly fall if the drug flops. Even though the stock's trading at an attractive forward price-to-earnings (P/E) multiple of 12, there are too many question marks surrounding the company to make it a buy. Amgen, meanwhile, offers investors a bit more predictability, and with a forward P/E of 13, it's not a whole lot more expensive.

Amgen's dividend yield of 3.1% is slightly lower than Gilead's annual payout of 3.6%, but both are still well above the S&P 500 average of 2%. There's not enough separating the two stocks when it comes to dividend or valuation, and that's why growth and stability need to be the deciding factors. With a new drug in its portfolio, Amgen has some exciting opportunities ahead. And even if remdesivir is successful in treating the coronavirus, that's not likely to generate sustainable, long-term growth for Gilead. Once vaccines are available, demand for the drug will likely disappear.

While it may be tempting to bet on a company working on a coronavirus drug, the safer, more reliable healthcare stock to go with is Amgen.