In D-cylcoserine studies with rats, the drug accelerated extinction learning, speeding the loss of conditioned fear responses. In human studies, D-cycloserine has also been shown to improve responses to two sessions of exposure therapy in patients with social phobia, and four sessions in patients with acrophobia.
"Based on the earlier work," the authors wrote, "we predicted that D-cycloserine would also facilitate the capacity of exposure therapy to weaken the link between obsession-related stimuli (e.g., public restrooms) and feared outcomes (e.g., contamination), thereby reducing associated fear responding (e.g., distress) along with the need for rituals (e.g., washing) and avoidance."
The investigators randomly assigned patients with OCD to receive either placebo (17 patients) or D-cycloserine (15 patients) at 125 mg for 10 doses, to be taken about two hours before each session of cognitive behavioral therapy.
The patients had twice weekly sessions of cognitive behavioral therapy for five weeks, with standard exposure/ritual prevention therapy techniques applied by a trained psychologist.