Axsome Therapeutics (AXSM) had the highest return in January 2019 by a mid-cap US stock, returning 198.6%.

ASSET	MONTH	% RETURN
Axsome Therapeutics (AXSM)	January 2019	198.58%
Enphase Energy (ENPH)	January 2019	56.16%
Griffon (GFF)	January 2019	56.13%
Novocure (NVCR)	January 2019	50.77%
Veracyte (VCYT)	January 2019	48.98%
Herc (HRI)	January 2019	47.9%
Vipshop (VIPS)	January 2019	44.55%
Cleveland-Cliffs (CLF)	January 2019	43.91%
ACADIA Pharmaceuticals (ACAD)	January 2019	43.81%
Companhia de Saneamento Basico do Estado de Sao Paulo SABESP ADR (SBS)	January 2019	43.81%
Boot Barn (BOOT)	January 2019	43.39%
Light & Wonder (LNW)	January 2019	43.28%
Century Communities (CCS)	January 2019	38.24%
Patrick Industries (PATK)	January 2019	37.82%
Modine Manufacturing (MOD)	January 2019	37.63%
Construction Partners (ROAD)	January 2019	37.4%
Blueprint Medicines (BPMC)	January 2019	36.64%
Carpenter Technology (CRS)	January 2019	36.43%
Bank Ozk (OZK)	January 2019	35.68%
Surgery Partners (SGRY)	January 2019	35.4%
RadNet (RDNT)	January 2019	35.15%
Comstock Resources (CRK)	January 2019	35.06%
Boyd Gaming (BYD)	January 2019	34.58%
TransAlta (TAC)	January 2019	34.32%
Mr Cooper (COOP)	January 2019	33.71%

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