Prediction: This Stock Has Soared Nearly 70% in 2025 and Will Be an Even Bigger Winner in 2026

Some stocks perform exceptionally well and garner lots of attention for it. They might even pick up catch nicknames like the "Magnificent Seven" stocks along the way. Other stocks, though, deliver tremendous gains, yet they remain under the radar for most investors.

Mirum Pharmaceuticals (NASDAQ: MIRM) is an excellent example of the latter category. This mid-cap stock has soared nearly 70% in 2025. I predict Mirum will be an even bigger winner in 2026.

Behind Mirum's meteoric rise

Although Mirum has three approved products on the market, one of them stands out as the company's primary growth driver. Sales for Livmarli soared 56% year-over-year in the third quarter of 2025 to $92.2 million. The drug accounted for approximately 69% of Mirum's total sales in the quarter.

The U.S. Food and Drug Administration (FDA) first approved Livmarli in September 2021 for the treatment of cholestatic pruritus (itching) in patients with Alagille syndrome. Only between 4,000 and 5,500 patients in the U.S. and the European Union have Alagille syndrome, a genetic disorder in which bile builds up in the liver due to the absence of enough bile ducts.

In 2024, Mirum secured two additional FDA approvals for Livmarli in a related disorder – one for treating patients aged five years or older with Progressive Familial Intrahepatic Cholestasis (PFIC) and the other expanding the label to include patients with PFIC aged 12 months or older. In April of this year, Mirum added FDA approvals for a tablet version of Livmarli in both Alagille syndrome and PFIC.

The company's two bile acid medicines – Cholbam and Ctexli – also continue to enjoy solid commercial success. Combined sales for these two drugs jumped 31% year-over-year in Q3 to $40.8 million.

Even better days ahead

I expect Mirum's momentum will accelerate next year. Livmarli is a key reason behind my optimism. In my view, the availability of a tablet formulation of the drug will boost sales. Peter Radovich, Mirum's president and COO, stated during the Q3 earnings call that the company is already seeing a "very encouraging" uptake for Livmarli tablets.

Mirum believes that Livmarli has the potential to generate annual sales exceeding $1 billion. I agree. But it's not the only potential blockbuster drug in the company's portfolio. Two pipeline candidates, voloxibat and MRM-3379, could also be massive winners.

Image source: Getty Images.

Volixibat is currently being evaluated in two Phase 2 clinical studies. Mirum expects to report topline data from a study targeting primary sclerosing cholangitis (PSC) in the second quarter of 2026. I look for these results to provide a solid catalyst for the biotech stock next year. The company should also complete enrollment in a second study targeting primary biliary cholangitis (PBC) in 2026, with topline results likely to be reported in the first half of 2027.

Mirum recently announced that the first patient has been enrolled in a Phase 2 study evaluating MRM-3379 for the treatment of patients with Fragile X syndrome (FXS). As is the case with PSC, there are no approved therapies for treating FXS. Although the company doesn't have plans to report any results from its Phase 2 study of MRM-3379, positive news from the volixibat Phase 2 study could increase excitement about the prospects for Mirum's third potential blockbuster.

What could derail my prediction?

I think that Mirum Pharmaceuticals will deliver a gain of more than 70% in 2026. My prediction could be derailed, though. If so, it will likely be because of one of two factors.

One possibility is that the results from the Phase 2 study of volixibat in PSC are disappointing. I don't expect this will be the case, especially since Mirum's interim analysis data was positive. However, there's still a chance that the data may not be as favorable as investors would prefer.

Another major factor that could cause my prediction to fall short is a steep overall stock market sell-off. It's difficult for any stock to rise in the midst of a significant market decline.

Even if Mirum's shares don't outperform the 2025 gains next year, I expect this stock to be a solid winner over the long term. Maybe, just maybe, it will garner more attention from investors at some point as well.

Keith Speights has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.