The results raised questions about a drug that is key to Vertex diversifying beyond its core cystic fibrosis treatments. Some analysts had said the painkiller might be a multibillion-dollar business for a company needing a next big driver of growth.

In a note to clients, Cantor analyst Olivia Brayer said the trial results are "without a doubt a setback" for the company. RBC Capital Markets analyst Brian Abrahams said the data "reflect a near worst-case scenario for this key pipeline program and raise considerable risk" around the drug's potential in chronic pain conditions.

Vertex shares fell as much as 16% when markets opened Thursday, marking their biggest intraday drop in four years. The stock had gained 10% this year through Wednesday.

'Clear Negative'

Stifel analyst Paul Matteis said the study result "looks like a pretty clear negative," adding that he was "confused" by the company's decision to advance the drug for that condition to a late-stage trial.

Even before this trial, some analysts questioned the drug's commercial potential, noting that health insurers and hospitals may still have incentives to steer patients to opioids, which are cheap and effective. Vertex has been pressing Congress to create new policies that level the playing field between its drug and opioids.

For 12 weeks, the study followed more than 200 patients with lumbosacral radiculopathy, a nerve condition in the lower back often called sciatica.

The trial hit its goal of a statistically significant change from baseline in a widely used measure of pain intensity.

In a call with analysts, Vertex Chief Executive Officer Reshma Kewalramani expressed optimism in the drug's potential in a late-stage trial because at some of the study sites, Vertex's drug did outperform the placebo.

'Well Tolerated'

The company said the drug was "generally well tolerated" with no serious adverse events.

Vertex's drug, suzetrigine, has been hailed as a scientific breakthrough because it blocks a sodium channel that helps control activity in the body's neurons, treating pain without entering the brain. That makes it less addictive than opioids, which were involved in about 70,000 overdose deaths for the year ending June 2024.

If approved, Vertex's drug would be the first new class of pain medication in more than two decades.