Verona Pharma PLC ADR (VRNA) had the highest return in December 2021 by a mid-cap US stock, returning 39.1%.

ASSET	MONTH	% RETURN
Verona Pharma PLC ADR (VRNA)	December 2021	39.13%
Hagerty (HGTY)	December 2021	38.88%
Roivant Sciences (ROIV)	December 2021	34.04%
Advantage Solutions (ADVWW)	December 2021	32.8%
Applied Blockchain (APLD)	December 2021	32.18%
TG Therapeutics (TGTX)	December 2021	30.58%
Jackson Financial (JXN)	December 2021	30.27%
Embraer SA ADR (ERJ)	December 2021	28.07%
Alpha Metallurgical Resources (AMR)	December 2021	27.8%
Intracellular Th (ITCI)	December 2021	27.5%
Laureate Education (LAUR)	December 2021	26.53%
Braskem SA Class A (BAK)	December 2021	25.71%
Pampa Energia SA ADR (PAM)	December 2021	24.95%
Trump Media & Technology (DJT)	December 2021	24.05%
ACADIA Pharmaceuticals (ACAD)	December 2021	22.78%
Alliance Resource Partners (ARLP)	December 2021	22.48%
Endeavor (EDR)	December 2021	22.25%
Merus (MRUS)	December 2021	21.79%
Halozyme Therapeutics (HALO)	December 2021	21.59%
LG Display (LPL)	December 2021	21.01%
Cushman & Wakefield (CWK)	December 2021	20.61%
Inter Parfums (IPAR)	December 2021	20.43%
Veren (VRN)	December 2021	20.28%
Century Aluminum (CENX)	December 2021	20.17%
Powell Industries (POWL)	December 2021	19.88%

Mid-cap stocks are treated as having a market cap between $2B and $10B.