No LD50 of standard St. John’s wort extract was identified in studies of mice, rats, and dogs treated for 26 weeks, even at dosages of 5,000 mg/kg [Schulz et al., 1998, p56]. Intolerance reactions appeared at 900 mg/kg/day. No genotoxic or mutagenic effects were noted in these studies.
St. John’s wort extract has also been shown to be antimutagenic in E. coli [Vukovic-Gacic et al., 1993]. However, it has been recognized that hypericin can accumulate in the nucleus of cells exposed to the compound and directly bind to DNA [Miskovsky et al., 1995]. The relevance of these findings is unclear, and no long-term carcinogenicity testing has been done with St. John’s wort.
St. John’s wort is generally very well tolerated. In the extensive German experience with St. John’s wort as a treatment for depression, no reports of serious adverse consequences or drug interactions have been published [De Smet et al., 1996]. In particular, no MAO-inhibitor-type reactions have ever been reported.
A drug monitoring study of 3,250 patients taking St. John’s wort extract for 4 weeks [Woelk et al., 1994] revealed an overall incidence of side effects of 2.4%. The most common were mild stomach discomfort (0.6%); allergic reactions, primarily rash (0.5%); tiredness (0.4%); and restlessness (0.3%). Only 1.5% of the patients dropped out of the study because of adverse reactions. For comparison, about 17% of patients on fluoxetine and 31% of patients given tricyclics stopped taking the drug because of side effects [Stokes, 1993]. Furthermore, as many as one in three patients on SSRIs develop symptoms of sexual dysfunction [Balon et al., 1993]. However, cross-study comparisons of this type are of questionable validity.
The overall incidence of side effects in the double-blind studies that compared St. John’s wort to a placebo was 4.1% [Linde et al., 1996].
Like other antidepressants, St. John’s wort may cause manic episodes in individuals with bipolar disorder.
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