Is the hierarchy necessary? Gradual versus variable exposure intensity in the treatment of unacceptable obsessional thoughts.

•Patients with unacceptable obsessions are at risk of return of fear after exposure.•EXP-G vs. EXP-V comparisons at 3-month follow-up were moderate in magnitude.•EXP-G maintained gains at 3MFU while EXP-V continued to improve.•Variability in subjective and physiological fear did not predict outcomes.