AbbVie (ABBV) had the worst day in Q3 2021 by a mega-cap US stock on September 1, 2021, returning -7.2%.

ASSET	DATE	% RETURN
AbbVie (ABBV)	9/1/2021	-7.21%
Palantir Technologies (PLTR)	9/28/2021	-6.22%
Crowdstrike (CRWD)	8/11/2021	-5.64%
Wells Fargo (WFC)	8/31/2021	-5.6%
Palantir Technologies (PLTR)	7/7/2021	-5.53%
Palantir Technologies (PLTR)	7/1/2021	-5.29%
Eli Lilly and (LLY)	9/9/2021	-5.25%
Crowdstrike (CRWD)	8/10/2021	-5.1%
Advanced Micro Devices (AMD)	9/28/2021	-4.98%
Wells Fargo (WFC)	9/1/2021	-4.92%
Micron Technology (MU)	8/10/2021	-4.9%
Advanced Micro Devices (AMD)	7/7/2021	-4.71%
International Business Machines (IBM)	7/2/2021	-4.69%
NVIDIA (NVDA)	7/16/2021	-4.57%
Oracle (ORCL)	9/30/2021	-4.52%
Philip Morris International (PM)	9/30/2021	-4.42%
ASML Holding NV ADR (ASML)	9/29/2021	-4.41%
Applied Materials (AMAT)	7/16/2021	-4.34%
NVIDIA (NVDA)	7/15/2021	-4.27%
Palantir Technologies (PLTR)	9/29/2021	-4.26%
Micron Technology (MU)	7/7/2021	-4.25%
Amgen (AMGN)	8/4/2021	-4.22%
Palantir Technologies (PLTR)	7/14/2021	-4.14%
GE Aerospace (GE)	9/14/2021	-3.98%
Lam Research (LRCX)	7/16/2021	-3.97%

Mega-cap stocks are treated as having a market cap of $200B+.