Ionis Pharmaceuticals Stock Slides 23% Over 8 Straight Down Days
A multi-day slide in the biotech’s stock has erased billions in value, focusing attention on its underlying business performance.
Ionis Pharmaceuticals (IONS) stock has now moved lower for 8 consecutive trading days, a slide that has cut its price by a cumulative 23%. That streak has erased about $2.3 billion from the company’s market value, which now stands at about $7.8 billion.
For anyone holding the stock, the slide deepens an already bad year: Ionis Pharmaceuticals is down 40.3% in 2026 and 36.1% over the past three months. Ionis Pharmaceuticals stock trades at about $47.25 a share as of 9/15/2026.
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 | -8.1% | -0.4% |
| 8D (Current Streak) | -23.0% | -1.1% |
| 1M (21D) | -17.5% | -2.6% |
| 3M (63D) | -36.1% | 0.4% |
| YTD 2026 | -40.3% | 10.8% |
| 2025 | 126.3% | 16.4% |
| 2024 | -30.9% | 23.3% |
| 2023 | 33.9% | 24.2% |
What do the fundamentals show?
The company’s recent performance shows signs of strain. Revenue over the last twelve months declined 7.4%, while its operating margin was -68.0%. For comparison, the median operating margin among S&P 500 Health Care stocks is 17.6%. The company also has negative trailing earnings, so it does not have a meaningful price-to-earnings multiple. The sell-off followed clinical trial disappointment, after partner Novartis reported that the Phase 3 Lp(a)HORIZON study for pelacarsen failed to achieve its primary endpoint.
While its 3-year average annual revenue growth is 12.5%, the recent selling in the stock is its own story. Over the same 8 trading days the S&P 500 returned -1.1%.
A streak is a signal, not a command.
A long streak in either direction is information. It tells you that a stock has captured the market’s attention and that momentum is a factor. It is not, however, an instruction to buy or sell. The disciplined response is to use the new price as a reason to re-evaluate the business. The numbers here offer a starting point for that work, weighing the company’s financial results against its new, lower valuation.
A sharp drawdown naturally raises the question: 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.