5. received at least two kinds of SSRIs at optimal dose for more than 12 weeks An optimal dose is described as following: clomipramine hydrochloride, at least 225 mg/d;fluoxetine, at least 60 mg/d; paroxetine hydrochloride, at least 60 mg/d; sertraline hydrochloride, at least 200 mg/d; fluvoxamine, at least 250 mg/d; citalopram hydrobromide,at least 60 mg/d; and escitalopram oxalate, at least 40 mg/d.Patients who are unable to tolerate the supposed optimal doses were also eligible if at their maximally tolerated dose.