Ionis Pharmaceuticals Stock Slides 27% Over 9 Straight Down Days
A nine-day slide has erased billions in value, and the company’s own numbers offer a place to start a review.
Ionis Pharmaceuticals (IONS) stock has fallen for 9 consecutive trading days, a cumulative loss of 27%. That move has erased about $2.7 billion from the company’s market value, which now stands at about $7.4 billion.
The stock trades at $44.84 a share as of 9/16/2026.
How the streak stacks up against the S&P 500
Here is how IONS stock stacks up against the S&P 500 over the streak and the periods around it:
| Return Period | IONS | S&P 500 |
|---|---|---|
| 1D | -5.1% | -0.4% |
| 9D (Current Streak) | -26.9% | -1.5% |
| 1M (21D) | -23.5% | -2.5% |
| 3M (63D) | -38.7% | 0.5% |
| YTD 2026 | -43.3% | 10.3% |
| 2025 | 126.3% | 16.4% |
| 2024 | -30.9% | 23.3% |
| 2023 | 33.9% | 24.2% |
How do the underlying numbers look?
The selling appears to be stock-specific. Over the same 9 trading days, the S&P 500 returned -1.5%. While recent selling was accelerated by partner Novartis reporting that pelacarsen missed its Phase 3 primary endpoint, the company’s underlying numbers were already showing pressure, with trailing twelve-month revenue down 7.4%.
Its operating margin over the same period is -68.0%, compared with an S&P 500 Health Care median of 17.6% Ionis also has negative trailing earnings. While its 3-year average annual revenue growth is 12.5%, the more recent figures point to contraction.
A streak is a signal, not a command.
A long streak of losses is information. It signals heavy, sustained selling pressure, but it does not tell an investor what to do next. The disciplined response is to check the business against the price.
A nine-day move can create a dislocation, but it can also be a rational repricing. The numbers here offer a starting point for that work, weighing the stock’s recent slide against its underlying financial results.
Sharp drawdowns like this pose an obvious follow-up: which marked-down stocks are actually worth buying? Our Buy the Dip screen runs that test every day, flagging beaten-down names whose fundamentals still hold up.
Prefer the theme to this single name? Our ETF Scorecard shows how the biotech funds stack up. Any one of those funds is still a concentrated bet on that one theme, though, which is exactly the gap the portfolio below closes.
A slide like this is why diversification exists
Watching one stock fall day after day is the clearest lesson the market teaches about single-name risk. Whether this particular decline is an opportunity or a warning, the deeper point is the same: no one name should be able to do this to your portfolio.
The Trefis High Quality (HQ) Portfolio is built on that principle: roughly 30 businesses selected for consistent cash generation, strong margins, and resilient balance sheets, sized and rebalanced with rules. It has a track record of outpacing a benchmark that combines the three major indices – the S&P 500, S&P Mid-cap, and Russell 2000. Study the slide; spread the risk.