Amgen's worst day in a year was only 15% of healthcare's $162 billion loss

Healthcare stocks in the S&P 500 lost a combined $162 billion in market value on September 8, the worst showing of any of the index's 11 sectors on a day the S&P 500 itself fell 0.54%.

The trigger was a single trial result. Novartis said its closely watched pelacarsen study, aimed at lowering Lp(a) - a cholesterol-related particle tied to heart disease - failed to meet its goal, the Wall Street Journal reported. $AMGN has its own Lp(a) candidate, olpasiran, working through a similar mechanism, and 24/7 Wall St reported that the Novartis failure clouded the entire drug class, sending Amgen down as much as 10% on the day.

Our own trading data confirms just how far outside Amgen's normal range that move was. $AMGN closed down 10.08% on September 8 - its worst single day of the past 260 trading sessions by a wide margin. The next-worst day in that stretch was a 4.75% decline on May 1, less than half the size. The stock's market cap fell from $236.4 billion to $212.6 billion, a one-day loss of $23.8 billion.

Novartis itself, which trades in the US as an ADR outside the S&P 500, fell even harder: 24/7 Wall St put the decline at 14%, larger than Amgen's own drop even though Novartis was the company whose trial actually failed.

The sector-wide reaction was broader than one drug

MarketWatch described the reaction as a broad biopharma stock selloff, and the site's own numbers back that up. Of the 59 Healthcare stocks in the S&P 500, 56 closed lower - 95% of the sector - against a median decline of 2.59%. That is a noticeably wider and deeper move than the S&P 500 as a whole, where 354 of 500 stocks (71%) fell and the median decline was 1.05%.

Amgen's $23.8 billion loss was real, but it was only about 15% of the sector's total $162 billion decline. Add $SYK, which fell 8.81% - also its worst day of the past year, beating a prior low of 6.47% on May 1 - and the market-cap loss reaches about $34 billion, still only around a fifth of the sector's total.

Stryker's drop had nothing to do with Novartis or cholesterol drugs. Business Upturn reported supply problems and weak joint-replacement sales weighing on the company's outlook, a separate and unrelated catalyst that happened to land on the same day.

The rest of the sector moved too

Big pharma names with no direct stake in the Lp(a) trial fell by comparable amounts: $LLY dropped 2.21%, $PFE fell 2.32%, $JNJ declined 2.22%, $REGN slid 2.10%, and $MRK was down 1.24%. None of those five had a headline reason tied to the Novartis result. Their declines were in line with - or larger than - the sector's 2.54% cap-weighted average, which is what turns a single failed trial into a sector-wide selloff rather than a one-stock story.

Healthcare's decline was more than four and a half times the size of the next-worst sector, Financials, and it was the only sector where fewer than 1 in 20 constituents closed higher.