Novartis experimental drug del-desiran fails Phase III study for myotonic dystrophy, shares plunge 9%

By Bhanvi Satija, Dave Graham, and Marleen Kaesebier Tue, September 8, 2026 at 4:26 AM PDT | 3 min read

Novartis announced on Tuesday that its experimental drug for a muscle-wasting disorder failed a late-stage study, marking the second major trial setback in days. The news sent the Swiss drugmaker's shares down approximately 9%, representing one of its worst trading days on record.

The setback involves del-desiran, which Novartis acquired through its recent $12 billion acquisition of Avidity. The failure increases pressure on CEO Vas Narasimhan and his M&A strategy to strengthen the company's pipeline.

The drug was being tested for myotonic dystrophy, a muscle-wasting disease for which no approved treatments currently exist.

Trial Dents Confidence in Novartis Pipeline

• Novartis shares fell more than 10% at one point and were headed for a record drop.
• The stock is now trading near its level at the start of the year.
• The slide has wiped approximately 24 billion Swiss francs ($29.6 billion) off the company's market value.

Barclays analysts had estimated peak annual sales of $3.1 billion for del-desiran and assigned the drug a 60% chance of success following positive Phase II data.

The results also weighed on other drug developers in U.S. premarket trading:

• Dyne Therapeutics shares fell 30%
• Sarepta Therapeutics shares fell 15.5%

Both companies are developing treatments for muscular dystrophy.

Investors had been counting on del-desiran, heart drug pelacarsen, and anti-inflammatory drug remibrutinib to drive growth as Novartis faces declining sales of older drug Entresto and prepares for patent expiries early in the next decade.

James Eugene, an analyst at Novartis shareholder Verso Investment Management, said the drug "should have been a 'must win' for the company," adding that the failure would put more pressure on dealmaking and other drugs in development.

"This recent setback would have dented confidence in its acquisition strategy given the size of the deal and the relatively high expectations of success for del-desiran."

The trial failure means Novartis has now missed on two of its three key pipeline readouts this year.

Pressure on CEO Narasimhan

The news adds pressure on Narasimhan, who has focused on rebuilding Novartis' pipeline after spinning off its generics and consumer businesses while confronting what he has called the company's steepest patent cliff in decades.

Despite the setbacks, Novartis reiterated its full-year guidance and continues to expect sales to grow at a compound annual rate of 5% to 6% between 2025 and 2030.

Shreeram Aradhye, Novartis' president of development and chief medical officer, said developing therapies for diseases such as myotonic dystrophy type 1 remained challenging and that setbacks were part of scientific progress.

Novartis stated that the Phase III HARBOR study on del-desiran failed to show a statistically significant improvement over placebo on the primary endpoint of video hand-opening time, a measure of hand myotonia.

The announcement came a day after Novartis shares fell more than 3% following the failure of its cholesterol drug in a closely watched study.

($1 = 0.8107 Swiss francs)

Reporting by Dave Graham, Bhanvi Satija, Marleen Kaesebier, and Sriparna Roy; Editing by Ludwig Burger and Mark Potter