Allegiance effects have been discussed, debated, and tested over the past several decades. The evidence clearly shows that allegiance affects the findings and representation of therapies that are considered efficacious. We argue that allegiance effects are evident in randomized controlled trials of supportive therapy. Supportive therapy is an established and bona-fide therapy but its implementation as a control group for non-specific elements is a treatment that does not resemble supportive therapy as would be used therapeutically. Allegiance effects in the use of supportive therapy are caused by the design of supportive therapy controls, the therapists who deliver supportive therapy, and the patients who are enrolled in the trials.