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Page: Drug Interactions
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Pharmacokinetic interactions
St John's wort has been shown to cause multiple drug interactions mainly through induction of the cytochrome P450 enzyme CYP3A4, but also CYP2C9. This results in the increased metabolism of those drugs, resulting in decreased concentration and clinical effect. The principal constituent thought to be responsible is hyperforin.
Examples of drugs causing clinically-significant interactions with St John's Wort Class Drugs
antiepileptics carbamazepine, phenytoin
antiretrovirals non-nucleoside reverse transcriptase inhibitors, protease inhibitors
benzodiazepines alprazolam, midazolam
hormonal contraception combined oral contraceptives
immunosuppressants calcineurin inhibitors, ciclosporin, tacrolimus
others digoxin, methadone, omeprazole, phenobarbitone, theophylline, warfarin
Reference: Rossi, 2005
Pharmacodynamic interactions
St John's Wort may also contribute to serotonin syndrome in combination with other drugs which may elevate 5-HT (serotonin) levels in the central nervous system (CNS).
Drugs which may contribute to serotonin syndrome with St John's Wort Class Drugs
antidepressants MAOIs, TCAs, SSRIs, mirtazapine, venlafaxine
opioids tramadol, pethidine
CNS stimulants phentermine, diethylpropion, amphetamines, sibutramine
5-HT1 agonists triptans
illicit drugs methylenedioxymethamphetamine (MDMA), lysergic acid diethylamide (LSD), cocaine
others selegiline, tryptophan, buspirone, lithium, linezolid, dextromethorphan,5-HTP
Reference: Rossi, 2005
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Important notice:
The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other
qualified health provider with any questions you may have regarding a medical condition.
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