From http://www.nutritionj.com/content/7/1/2 , "Nutritional Therapies for mental health disorders"

Obsessive-Compulsive Disorder

Obsessive compulsive disorder (OCD) is an anxiety disorder that causes recurring stressful thoughts or obsessions that are followed by compulsions, which are repeated in an uncontrollable manner as a means of repressing the stressful thought [66]. It is well documented that selective serotonin reuptake inhibitors (SSRIs) help patients with OCD [67]. Therefore, it is clear that nutrients which increase serotonin levels will reduce the symptoms of OCD. As discussed earlier, the amino acid tryptophan is a precursor to serotonin, and tryptophan supplements (which are better than 5-Hydroxytryptophan) will increase serotonin levels and treat OCD [68].

A commercially available supplement called Amoryn has recently proven to help patients suffering from depression, anxiety, and OCD [69,70]. The main ingredient in Amoryn, St. John's wort, has been shown to help OCD patients better deal with their recurring thoughts and compulsions. Two double-blind, placebo-controlled studies were recently performed that compared the affects of a 900 mg daily dose of St. John's wort extract to 20 mg daily doses of Paroxetine (Paxil) or Fluoxetine; which are both SSRIs used to treat OCD. In comparison to patients taking Paxil, those who took the St. John's wort supplement showed a 57% decrease in OCD symptoms and were 47% less likely to exhibit side effects [69]. In comparison to patients taking Fluoxetine, consumption of the St. John's wort extract reduced 48% of OCD patient's symptoms [70]. These results clearly depict how the use nutritional supplements can be effective treatments for mental disorders.