AbbVie (NASDAQ:ABBV) is basically a one-trick pony. The trick is an immunosuppressant called Humira, prescribed to fight rheumatoid arthritis and other conditions. It’s the best-selling drug in the world, bringing in $18.4 billion in 2017, but that might not be sufficient to support the future of AbbVie stock.

While protected against direct competition in the U.S. until 2023, Humira is already facing biosimilars in Europe, as its protections there disappear.

AbbVie has been milking Humira for dividends, $4.28 per year, a yield of 4.76%. The stock looks cheap, at 18 times earnings, and has held up well during the bear market, down just 8.7% over the last six months while the average NASDAQ stock is down nearly 15%.

The question for investors is whether AbbVie stock is the kind of defensive play you want to be making in 2019.

AbbVie Stock Shows Signs of Life

Like an aging doyenne who can still dance at the ball, AbbVie’s situation still looks good.

Despite a price tag of up to $2,600 per month, Humira continues to sell because it has been approved to treat many diseases. Not just arthritis, but Crohn’s Disease, ulcerative colitis and even the heartbreak of psoriasis are treated with it.

While its U.S. patent expired in 2016, AbbVie has been able to extend its U.S. rights into the next decade through ancillary patents and aggressive lawyering. Rather than ending, its sales are expected to just trend down slowly.

While Europe this year will have biosimilars from privately-held Boehringer Ingelheim, Sandoz, Amgen (NASDAQ:AMGN) and Samsung Bioepis, Humira’s revenues won’t be destroyed, only reduced.

AbbVie, which was spun out of Abbott Laboratories (NYSE:ABT) in 2013, has also been building its own drug pipeline, with  new dermatology drugs on the way, as well as anti-cancer drugs. It has a treatment for Hepatitis C, Mavyret, which competes directly with Harvoni from Gilead Sciences (NASDAQ:GILD).

The Long Look at AbbVie Stock

Still, like that old doyenne, AbbVie knows the sunset for Humira is coming. It’s like an old oil field. You can frack it, but those wells, too, won’t produce forever.

Early in the next decade, AbbVie will be facing a problem similar to the one Pfizer (NYSE:PFE) did early in this decade, when the rights on Lipitor expired in 2011. There are a host of strategies for keeping such drugs alive, in a financial sense, and AbbVie is engaging in, or preparing to engage, in all of them.

But Humira is as dominant as Lipitor once was, with twice the sales of the next largest-selling drug, Celgene’s (NASDAQ:CELG) Revlimid, a cancer drug. AbbVie will need several hits to replace Humira, and time is running out.

AbbVie is the big winner in immunosuppressants, originally developed to prevent rejection of new organs but now offered against a host of autoimmune conditions, but as its own experience with Mavyret shows, European regulators and American pharmacy benefit managers have ways to fight back against skyrocketing prices.

The effectiveness of these tools, pitting drug against drug and choosing a formulary based at least partly on price, is going to increase with competition over the coming years and may be a bigger overhang on AbbVie’s growth than its patent expiration.

The Bottom Line on AbbVie Stock

For now, the good times roll on. AbbVie is due to report earnings Jan. 25, expecting sales of $8.36 billion for a 2018 total of $32.8 billion , 16% ahead of 2017’s $28.2 billion. Net income of $1.92 per share will bring that total to $6.92 per share for the year.

But, as they say of both athletes and great beauties, Father Time is undefeated. AbbVie still faces a patent cliff, and growing opposition to rising prices. Nothing lasts forever. What works this year may not work next year. Know that before you buy AbbVie stock.

Dana Blankenhorn is a financial and technology journalist. He is the author of a new mystery thriller, The Reluctant Detective Finds Her Family, available now at the Amazon Kindle store. Write him at danablankenhorn@gmail.com or follow him on Twitter at @danablankenhorn. As of this writing he owned no shares in companies mentioned in this article.