An isolated antibody or a binding fragment thereof, which binds to olanzapine and which is selected from the group consisting of: i) an isolated antibody or a binding fragment thereof comprising: a) the light chain CDR1 sequence comprises amino acid residues 44 to 54 of SEQ ID NO:11; b) the light chain CDR2 sequence comprises amino acid residues 70 to 76 of SEQ ID NO:11; c) the light chain CDR3 sequence comprises amino acid residues 109 to 117 of SEQ ID NO:11; d) the heavy chain CDR1 sequence comprises amino acid residues 45 to 54 of SEQ ID NO:12; e) the heavy chain CDR2 sequence comprises amino acid residues 69 to 85 of SEQ ID NO:12; and f) the heavy chain CDR3 sequence comprises amino acid residues 118 to 122 of SEQ ID NO:12; or ii) an isolated antibody or a binding fragment thereof comprising: a) the light chain CDR1 sequence comprises amino acid residues 44 to 54 of SEQ ID NO:15; b) the light chain CDR2 sequence comprises amino acid residues 70 to 76 of SEQ ID NO:15; c) the light chain CDR3 sequence comprises amino acid residues 109 to 117 of SEQ ID NO:15; d) the heavy chain CDR1 sequence comprises amino acid residues 45 to 54 of SEQ ID NO:16; e) the heavy chain CDR2 sequence comprises amino acid residues 69 to 85 of SEQ ID NO:16; and f) the heavy chain CDR3 sequence comprises amino acid residues 118 to 122 of SEQ ID NO:16. i) an isolated antibody or a binding fragment thereof comprising: a) the light chain CDR1 sequence comprises amino acid residues 44 to 54 of SEQ ID NO:11; b) the light chain CDR2 sequence comprises amino acid residues 70 to 76 of SEQ ID NO:11; c) the light chain CDR3 sequence comprises amino acid residues 109 to 117 of SEQ ID NO:11; d) the heavy chain CDR1 sequence comprises amino acid residues 45 to 54 of SEQ ID NO:12; e) the heavy chain CDR2 sequence comprises amino acid residues 69 to 85 of SEQ ID NO:12; and f) the heavy chain CDR3 sequence comprises amino acid residues 118 to 122 of SEQ ID NO:12; or a) the light chain CDR1 sequence comprises amino acid residues 44 to 54 of SEQ ID NO:11; b) the light chain CDR2 sequence comprises amino acid residues 70 to 76 of SEQ ID NO:11; c) the light chain CDR3 sequence comprises amino acid residues 109 to 117 of SEQ ID NO:11; d) the heavy chain CDR1 sequence comprises amino acid residues 45 to 54 of SEQ ID NO:12; e) the heavy chain CDR2 sequence comprises amino acid residues 69 to 85 of SEQ ID NO:12; and f) the heavy chain CDR3 sequence comprises amino acid residues 118 to 122 of SEQ ID NO:12; or ii) an isolated antibody or a binding fragment thereof comprising: a) the light chain CDR1 sequence comprises amino acid residues 44 to 54 of SEQ ID NO:15; b) the light chain CDR2 sequence comprises amino acid residues 70 to 76 of SEQ ID NO:15; c) the light chain CDR3 sequence comprises amino acid residues 109 to 117 of SEQ ID NO:15; d) the heavy chain CDR1 sequence comprises amino acid residues 45 to 54 of SEQ ID NO:16; e) the heavy chain CDR2 sequence comprises amino acid residues 69 to 85 of SEQ ID NO:16; and f) the heavy chain CDR3 sequence comprises amino acid residues 118 to 122 of SEQ ID NO:16. a) the light chain CDR1 sequence comprises amino acid residues 44 to 54 of SEQ ID NO:15; b) the light chain CDR2 sequence comprises amino acid residues 70 to 76 of SEQ ID NO:15; c) the light chain CDR3 sequence comprises amino acid residues 109 to 117 of SEQ ID NO:15; d) the heavy chain CDR1 sequence comprises amino acid residues 45 to 54 of SEQ ID NO:16; e) the heavy chain CDR2 sequence comprises amino acid residues 69 to 85 of SEQ ID NO:16; and f) the heavy chain CDR3 sequence comprises amino acid residues 118 to 122 of SEQ ID NO:16.