Flumazenil (brand name Romazicon) is a benzodiazepine antagonist with chemical formula C₁₅H₁₄FN₃O₃, belonging to the imidazobenzodiazepine class. It blocks the effects of benzodiazepines by competitively inhibiting activity on the GABA receptor complex. Because of this action, it is used in cases of a benzodiazepine overdose.

Chemical structure:

               O  H   H
               \\  \ /
      H    N    C   C   H
       \ //  \ / \ / \ /
        C     C   O   C--H
         \   //        \
   H  H   N--C   H      H
    \  \ /    \ /
     C==C      C--H
    /    \     /
H--C      C   N
   \\    //\ / \
     C--C   C   C--H
    /  /    ||  |\
   F  H     O   H H

Sources:
http://www.chemagis.co.il/prod7.htm
http://www.rxlist.com/cgi/generic3/flumazenil_cp.htm