Amylyx Pharmaceuticals Jumps 64% as Biotech Breakthroughs Lead Today's Stock Gainers · Aug 18, 2026

Which US stocks moved most on August 18, 2026, the themes that drove them, and the news behind each move.

1. Market at a glance

- S&P 500 (SPY) 767.36 ▼ −0.4% - Nasdaq 100 (QQQ) 717.51 ▼ −0.1% - Russell 2000 (IWM) 300.19 ▼ −0.3% - Dow (DIA) 532.93 ▼ −0.8%

2. Biggest movers, grouped by what drove them

💊 Biotech Breakthroughs — Amylyx Pharmaceuticals surged after its avexitide Phase 3 trial met primary endpoints, reducing severe hypoglycemic events by 55%. - AMLX +63.8% — Amylyx Pharmaceuticals, Inc. - NUVB +7.3% — Nuvation Bio Inc. - LEGN +6.2% — Legend Biotech Corporation - PBLS +5.7% — Parabilis Medicines, Inc. - SRRK +5.1% — Scholar Rock Holding Corporation 🏥 Healthcare Earnings — Haemonetics beat Q1 earnings estimates with raised guidance, putting fair value back in focus for the healthcare sector. - HAE +16.0% — Haemonetics Corporation - HTFL +7.8% — Heartflow, Inc. - PODD +6.0% — Insulet Corporation - BHC +5.2% — Bausch Health Companies Inc. ⚡ Energy & Infrastructure — Targa Resources spiked after securing long-term ExxonMobil agreements, capitalizing on AI-driven data center power demand. - UGI +9.5% — UGI Corporation - TRGP +7.1% — Targa Resources Corp. 💻 SaaS & Software — No news attached — a flow move, not a catalyst. - DUOL +7.3% — Duolingo, Inc. - CCC +6.7% — CCC Intelligent Solutions Holdings Inc. - MNDY +5.7% — monday.com Ltd. - HUBS +5.1% — HubSpot, Inc. - WIX +4.7% — Wix.com Ltd. 💳 Financial Services & Payments — No news attached — a flow move, not a catalyst. - FRHC +6.9% — Freedom Holdings Corp. - FOUR +5.3% — Shift4 Payments, Inc. 🛍️ Consumer & Retail — No news attached — a flow move, not a catalyst. - BBWI +6.6% — Bath & Body Works, Inc. - PLNT +5.4% — Planet Fitness, Inc. - ULTA +4.7% — Ulta Beauty, Inc. 📈 Low-Priced Small Caps — No news attached — a flow move, not a catalyst. - DOO +7.5% — BRP Inc. - CHRN +6.0% — ChronoScale Holdings Corporation - BVC +5.7% — BitVentures Limited - DAO +5.7% — Youdao, Inc. - CLBT +5.4% — Cellebrite DI Ltd. - CLMT +5.1% — Calumet, Inc. - PSNY +4.7% — Polestar Automotive Holding UK PLC

3. What drove the upside

- Amylyx Phase III Avexitide Trial Cuts Severe Hypoglycemic Events 55% - Haemonetics (HAE) Earnings Beat Puts Fair Value Back In Focus - Targa Secures Long-Term ExxonMobil Agreements Across the Permian

4. What weighed on it

- KLAR −22.8% — Klarna Group plc - AEHR −15.4% — Aehr Test Systems, Inc. - One group moved with no news attached — flow, not a catalyst.

5. How this was built

Warrants and leveraged ETFs were removed before grouping — they crowd out the underlying names they track. 50 tickers survived that filter. Every number here comes from market data. The theme names and the one-line explanations are written from the day's headlines — where a group moved with no headline behind it, we say so rather than inventing a reason. This is an observation of what moved, not advice and not a recommendation. This tells you where attention went today; it does not tell you what happens next.