The STAR*D study (2006) was the largest and longest study ever conducted to evaluate depression treatment. It found that, after 12 to 14 weeks of treatment with citalopram (Celexa) 33% of the participants reached remission and about 14% more responded, but did not reach remission
One study found that, after 6 weeks of therapy with moderately depressed patients, 54.2 % responded to hypericum extract (St. Johns Wort), 55.9 % responded to citalopram, and 39.2 % responded to placebo. Thus this study found that citalopram and St. Johns Wort were equally effective, and that citalopram was only 15% more effective than placebo. - Gastpar M, Singer A, Zeller K (2006).