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St. John's wort and serotonin syndrome

From AAFP article:

Adverse Effects, Contraindications, and Drug Interactions

Because of the possibility of developing serotonin syndrome, use of St. John's wort in conjunction with selective serotonin reuptake inhibitors is not recommended. St. John's wort should be used cautiously in patients with bipolar disorder because there have been a few case reports of St. John's wort-related mania.28

Table 229-40 lists the possible drug interactions that may occur with St. John's wort. The results of one report41 suggest that induction of cytochrome (CYP) P450 3A4 activity by St. John's wort may have a substantial impact on the effectiveness of pharmaceutical agents because at least one half of all marketed medications are metabolized via this pathway.

Given the induction of CYP 3A4, concurrent use of St. John's wort may reduce the effectiveness of oral contraceptives. In a study35 of 12 healthy premenopausal women who received an oral contraceptive along with 900 mg of St. John's wort daily in three divided doses, researchers noted a shorter estrogen half-life and increased breakthrough bleeding. Women using oral contraceptives should be counseled regarding possible breakthrough bleeding and might consider a barrier method of contraception when taking St. John's wort.35

Additional study is needed to establish if and how St. John's wort interacts with specific pharmaceutical agents. Experience to date suggests few clinically significant interactions. Until the results of ongoing studies on this matter have been published, the medications listed inTable 229-40 should be considered to have potential interactions and should be monitored when used concurrently with St. John's wort. Family physicians should query all patients about the use of St. John's wort and other herbal agents.

Also

Dosage

Findings suggest that 900 mg of St. John's wort (450 mg two times daily or 300 mg three times daily) is needed to reduce symptoms of depression.8,10,17 Because plasma levels continue to show a gradual rise over several weeks, the full clinical effect of St. John's wort may take two to four weeks to manifest.