Despite the real problems with the additional indication being sought for suzetrigine, this drop in the stock is still an unambiguously appealing opportunity to buy the dip. Overall, Vertex's data on the candidate's efficacy for general acute pain look better than the new data on acute pain in a specific disease context.

Shares of Vertex Pharmaceuticals Inc. VRTX slid 0.46% to $408.76 Friday, on what proved to be an all-around rough trading session for the stock market, with the S&P 500 Index SPX falling 1.11% to 5,970.84 and Dow Jones Industrial Average DJIA falling 0.77% to 42,992.21. The stock's fall snapped a four-day winning streak.

Vertex Pharmaceuticals shares sank Thursday after the company reported mixed results in a Phase 2 drug trial to treat lumbosacral radiculopathy (LSR), which causes leg and back pain.

Different genetic mutations cause different problems with this particular protein -- so CFTR modulators generally don't work on every CF case. But Vertex's newest blockbuster, Trikafta -- approved in 2019 -- made a splash when it entered the market because it can be used for about 90% of patients with the disease.

This was the stock's fourth consecutive day of gains.