OBJECTIVETo assess individual difference characteristics of subgroups of patients with fibromyalgia (FM) patients with respect to the decision to stay in or switch from randomly-assigned verum or placebo treatment during an optional crossover phase of a double-blinded homeopathy study.DESIGNDouble-blinded, randomized, placebo-controlled, optional crossover clinical trial.PARTICIPANTSFifty-three (53) community-recruited patients with FM entered the optional crossover phase.INTERVENTIONTwo homeopaths jointly selected an individualized homeopathic remedy for all patients. The pharmacy dispensed either verum LM remedy or indistinguishable placebo in accord with randomized assignment for 4 months and the patient's optional crossover decision for an additional 2 months.OUTCOME MEASURESPatients completed a battery of baseline state/trait questionnaires, including mood, childhood neglect and abuse, and trait absorption. They rated global health (whole person-centered) and tender point pain on physical examination (disease-specific) at baseline, 3 months, and 6 months.RESULTSRates of optional crossover from verum to placebo or placebo to verum were comparable (p = 0.6; 31%, and 41%, respectively). The switch subgroups had greater baseline psychologic issues (emotional neglect in placebo-switch; depression and anger in verum-switch). The verum-stay subgroup scored highest on treatment helpfulness and included all six exceptional responders who fell, prior to crossover, into the top terciles for improvement in both global health and pain. Patients staying in their randomly assigned groups, active or placebo (n = 34), scored significantly higher in trait absorption than did those who switched groups (n = 19).CONCLUSIONIndividual difference factors may predict better and poorer responders with FM to specific and nonspecific effects of homeopathic and placebo treatment.