M99 or M-99 may refer to: Places M-99 (Michigan highway), a state highway in south central Michigan Messier 99, an unbarred spiral galaxy approximately 60 million light-years away in the constellation Coma Berenices M99 road (Johannesburg), Metropolitan route in the City of Johannesburg, South Africa Rifles Barrett M99, a sniper rifle Zijiang M99, a Chinese anti-materiel rifle Tranquilizer Etorphine (a.k.a. Immobilon or M99), a veterinary tranquilizer