Disclosed is an antibody or a binding fragment thereof which binds to quetiapine, which can be used to detect quetiapine in a sample such as in a competitive immunoassay method. The antibody or the fragment thereof can be used in a lateral flow assay device for point-of-care detection of quetiapine, including multiplex detection of aripiprazole, quetiapine, olanzapine, and risperidone in a single lateral flow assay device.