• May cause phototoxicity, photsensitivity or photoallergy ⁴⁵ Hypersensitivity reactions (which are more likely to occur in individuals who have previously demonstrated photsensitivity and in those with a history of allergies) such as blistering after sun exposure, worsening of sun burns, and contact allergic dermatitis even in the absence of light. It is not unusual for there to be an initial incubation period of 12 to 24hours before symptoms occur. All reactions are aggravated when exposed to sunlight. Severe skin reactions have been reported in AIDS patients. ⁸⁶
• Gastrointestinal irritation ⁵⁴
• Nausea ⁵⁴
• Dizziness ⁵⁴
• Acute neuropathy (rare) ⁸³
• Tiredness ⁸⁴
• Restlessness ⁸⁴
• Headaches ⁸⁴
• St John's Wort has been shown to be poisonous in very large quantities to animals. Also, photosensitivity in animals had been demonstrated. ⁷⁹

As with all Herbs and Drugs, the potential for interaction by a variety of mechanisms (e.g., pharmacodynamic, pharmacokinetic drug inhibition or enhancement, etc) are possibilities.

"While studies suggest fewer adverse effects compared with conventional antidepressants, there have been several recent reports suggesting important drug interactions with OCs, warfarin, cyclosporin and theophylline. Hypericum-containing products appear to induce hepatic enzymes of the cytochrome P450 group. In each of the reported cases, the patient has been female, though more women than men take hypericum extracts. Levels of the coadministered agent were reduced in each case report, and all such agents are metabolised by the P450 enzymes. Four in-vitro studies indicate hypericum extracts are capable of inducing and approximately doubling cytochrome P450 activity. In one study involving human volunteers, area under the curve for phenprocoumon was markedly reduced when patients were pretreated with hypericum extract compared with placebo. In another similar study serum digoxin levels that were previously stable fell increasingly with number of days on coadministered hypericum extract. Last year there were reports of central serotonin excess in five patients taking SSRIs as well as hypericum extracts. Patients were elderly and in each case symptoms such as altered mental status, tremor, GI upset, headache, myalgia and restlessness were serious." ⁸⁷

• According to information available on herb interactions, St. John's Wort extracts should not be used while taking other prescription anti-depressants or narcotics without physician approval. ⁸²

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