There is preliminary evidence to suggest that physical exercise may be beneficial for people with single disorder OCD. One pilot study of people with OCD maintained on SSRIs found an improvement in self- reported OCD symptoms and depression after six weeks of a walking intervention, which remained stable for one month post–treatment [799]. A second study found that the combination of a 12-week moderate aerobic exercise program with psychotherapy or pharmacotherapy reduced OCD symptom severity, which was maintained at 6-month follow-up [800]. The study found that significantly lower OCD symptoms, anxiety, and negative mood levels were reported immediately following each 20–40 minute exercise session, compared to the beginning of the session [801]. However, there is no evidence to date on the efficacy of physical exercise for the treatment of comorbid OCD and AOD use disorder specifically.