Within the field of adult mental health, self-help is now a pivotal treatment modality. However, earlier research indicates that some individuals react negatively to this. Through three, small-scale studies, this paper explores both clinicians’ experience of harm in patients as a response to self-help materials as well as patients’ own reports. In Study 1, a postal survey was administrated to clinicians; in Study 2, semi-structured interviews were conducted with clinicians; and in Study 3, patients were sent a postal survey. Over 18% of clinicians indicated that they had experienced self-help materials resulting in harm to patients. The interviews uncovered four main themes: the patients’ clinical presentation, how the materials were presented within the therapeutic contact, certain personality characteristics in patients, and the characteristics of some materials. Between 12% and 24% of patients reported experience of negative effects (depending upon how this is defined), although the latter finding is limited by a small sample size. Proposals are made that are linked to best practice and it is suggested that there is a generic training need for clinicians in materials’ use.