The U.S. Federal Trade Commission (FTC) allowed Amgen's (AMGN 1.00%) purchase of Horizon Therapeutics to go through last month and the company announced the closing of the deal in a press release last week. The FTC filed a lawsuit back in May opposing the deal as the government worried the merger would hurt competition, but it eventually backed off that position.

Now that the deal is complete investors can expect some enhanced growth potential on the horizon for Amgen. Is that enough reason to buy this healthcare stock?

What the deal does for Amgen

The acquisition of Horizon Therapeutics gives Amgen access to an incredibly promising drug called Tepezza, which patients use for thyroid eye disease. At its peak, the drug is forecast to bring in close to $3.9 billion in annual revenue by 2028. 

To put that into perspective, consider that Amgen's top-selling drug, Enbrel, which treats rheumatoid arthritis, generated $4.1 billion in sales last year. It is losing patent protection before the end of the decade, however, and so its revenue is expected to decline in the future. For Amgen, securing Tepezza can help to offset that.

It also gets much more than just Tepezza. Gout drug Krystexxa and Uplizna, which is a treatment for neuromyelitis optica spectrum disorder, are two promising assets from Horizon that Amgen management believes can help diversify the company's rare disease portfolio as well.

Last year, Horizon Therapeutics generated revenue of $3.6 billion and reported a profit of $521.5 million. Through the first six months of this year, the company's revenue has been flat at less than $1.8 billion, with Tepezza, Krystexxa, and Uplizna accounting for $1.4 billion of that total. 

The company's strong financials mean that the deal will immediately add to Amgen's bottom line with the company expecting a boost to both its top line and its adjusted earnings per share next year. Amgen says it will also update its guidance for the current year when it releases its third-quarter numbers, which are likely to come out next month.

Acquisitions are nothing new for Amgen, but they come at a steep cost -- rising debt

The Horizon Therapeutics deal is the largest one Amgen has made in recent years, but the company has been more than comfortable when it comes to wheeling and dealing. Last year, it acquired ChemoCentryx for $3.7 billion. In that acquisition, it locked up Tavneos, which is a treatment for anti-neutrophil cytoplasmic autoantibody-associated (ANCA) vasculitis. A few years back, in 2019, Amgen made a fairly large splash when it agreed to pay $13.4 billion to acquire the psoriasis drug Otezla from Celgene (now a subsidiary of Bristol Myers Squibb).

But a concern for investors is that as Amgen is acquiring assets, it is also relying on debt to help fund its growth strategy. The company's already high debt soared even higher this year.

AMGN Total Long Term Debt (Quarterly) Chart

AMGN Total Long Term Debt (Quarterly) data by YCharts

The company also needs more growth

Another problem with Amgen in the past was the lack of a strong growth rate. Over the past five years, the company's growth rate was mild, normally not more than a few percentage points. That's not going to get growth investors too excited about the business.

AMGN Revenue (Quarterly YoY Growth) Chart

AMGN Revenue (Quarterly YoY Growth) data by YCharts

As Enbrel loses patent protection and its revenue falls, the danger is that Amgen's growth rate may deteriorate even further. This is why it's crucial for Amgen to look for acquisitions and new growth opportunities. Without that, the company's top and bottom lines could come under pressure, and that could lead to the company also having to slash or stop its dividend payments. Plus, the company needs to show investors that the rising debt is worth it, and that it is paying off in the form of growth.

Is Amgen stock a buy?

Year to date, Amgen's stock is up an underwhelming 3%. Over a span of five years, it's up by just 32% in value while the S&P 500 managed gains of 52%. Amgen hasn't made for a great investment in the past, but with the company working on developing its pipeline and adding assets into its portfolio, it's paving the way for much growth in the years ahead. But with a high debt load, there's also plenty of pressure for the business to generate significant earnings growth in order to improve its financials and pay down some of that debt -- quickly.

The stock trades at 18 times earnings, which is mild compared with the healthcare industry average of 26. But investors are clearly discounting the stock given the risk it possesses right now. With interest rates potentially still rising higher, this is not a time when investors want to see high debt levels. 

Amgen is a bit of a risky buy at the moment, but given its cheap price, it has the potential to deliver some great returns in the long run. The safe option, however, would be to wait for a few more quarterly results to see how the healthcare company is managing and what its financials look like after the dust settles from its most recent transaction.