AbbVie (ABBV -0.76%) has shown itself to be a great long-term investment. The drugmaker's shares have climbed about 300% over the past decade. And earnings have soared, thanks to the company's blockbuster immunology drug Humira.

But things are changing at AbbVie. Humira already has been facing competition internationally, and that has weighed on sales. As of this year, it also faces competition in the U.S. This will clearly hurt earnings. In fact, management predicts a 37% drop in U.S. Humira sales this year. So now the question is: Is it too late to buy AbbVie stock? Let's find out.

Peak sales of $20 billion

Humira is a massive blockbuster due to its use across a range of illnesses, including rheumatoid arthritis and Crohn's disease. In 2021, Humira achieved peak annual revenue of more than $20 billion. That's more than 36% of the company's total revenue.

So there's reason for investors to be concerned about the emergence of competition and the forecast for declining Humira revenue. But there's also reason to see this as a temporary problem, and one with a solution just ahead -- AbbVie's newer immunology drugs Rinvoq and Skyrizi.

The company has been prepping these two products for a while to take over where Humira leaves off. And the plan is working. The company aims to win authorizations for these drugs in all of Humira's indications and more. So far, regulators have approved Rinvoq in five indications -- and they're reviewing it for a sixth, Crohn's disease, right now. As for Skyrizi, it has won three approvals and is in a phase 3 trial for ulcerative colitis.

But these drugs aren't only winning approvals. They are also winning over doctors and patients. In the most recent quarter, Skyrizi's net revenue soared 76% and Rinvoq's net revenue climbed 49%.

Both drugs brought in blockbuster revenue last year. And they're on the way to meeting AbbVie's big goal: The company says that together, they will generate more than $21 billion in annual revenue by 2027. That means they'll actually top Humira.

And as soon as 2025, the two drugs combined should bring in more than $17.5 billion in revenue. So this year might not be a big one for growth at AbbVie, but we might not have to wait very long for growth to take off again -- thanks to Rinvoq and Skyrizi.

Other blockbusters

It's also important to remember the other blockbusters in AbbVie's portfolio and its pipeline. The company has strengths in several treatment areas, but here I'll mention neuroscience and aesthetics in particular.

Last year, AbbVie's neuroscience portfolio posted double-digit growth to deliver more than $6.5 billion in revenue. The company sells products to treat migraine and major depressive disorder, for example.

AbbVie also sells the market-leading aesthetics products Botox wrinkle treatment and Juvederm filler. The company recently said it sees significant long-term growth potential for the aesthetics market. And that's logical considering the market is expected to expand by double digits throughout this decade.

Over time, AbbVie has increased earnings and it has a great track record.

ABBV Net Income (Annual) Chart

ABBV net income (annual) data by YCharts.

We can expect a pause in growth this year or next year as AbbVie transitions through the loss of Humira exclusivity. But considering the company's strong portfolio of drugs and full pipeline, its growth story is far from over -- it's just in a state of transition. Meanwhile, it trades for about 13 times forward earnings estimates, which seems reasonable for a company with solid long-term prospects.

All of this means it isn't too late to buy AbbVie stock. In fact, right now, during this transition period, is a good time to get in on the story for a bargain -- and benefit from the company's new phase of growth over the long haul.