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Drugs and Health Products
Drug interactions with Natural Health Products: A Discussion Paper (November 2001)
Appendix 1. Theoretical and/or reported drug interactions with St. John's wort4
| AnestheticsT,H(93) | May intensify or prolong activity | |
|---|---|---|
| AnticoagulantsT(25, 36) | May decrease anticoagulant effect | St. John's wort induces CYP3A4 |
| AnticonvulsantsT(36) (phenytoin, carbamazepine, phenobarbital) |
May decrease activity because of reduced blood levels | St. John's wort induces CYP450 |
| AntihypertensivesT(6) | May be additive reduction in pressure | St. John's wort may have a hypotensive effect |
| Beta blockersT(94) | Drug levels may theoretically be reduced | St. John's wort induces cytochrome P450 |
| Calcium channel blockersT(24) | Drug levels may theoretically be reduced | Drug levels may theoretically be reduced |
| CyclosporinH(18, 95) (tacrolimus) |
Decreased blood levels of cyclosporin | Induction of CYP3A4 Induction of P-glycoprotein |
| DigoxinH(96) | Decrease levels of digoxin | May be through induction of P-glycoprotein May apply to other drugs that are partially eliminated by P-glycoprotein (e.g., Ca channel blockers, lidocaine, amiodarone, cyclosporin, doxorubicin, quinidine)T(96) |
| DiltiazemT(24) | Drug levels may theoretically be reduced | Drug levels may theoretically be reduced |
| IndinavirH(34) | Indinavir levels were significantly reduced in healthy patients | St. John's wort induces cytochrome P450 Other protease inhibitors? |
| Nonnucleoside reverse transcriptase inhibitors (nevirapine)T(34) |
Drug levels may theoretically be reduced | St. John's wort induces cytochrome P450 |
| Oral ContraceptivesT(36, 97) | May decrease blood levels of OC | St. John's wort induces cytochrome P450 |
| SSRIs(paroxetine)H(30) sertraline, nefazodoneH(37) |
May produce additive effects | May cause serotonin syndrome |
| TheophyllineH(98) | May decrease blood levels of theophylline | St. John's wort induces cYP450 (1A2) May affect other substrates for CYP1A2 (e.g., clozapine, olanzapine, clomipramine, imipramine)T(98) |
T = theoretical, based on constituents or mechanism of action,
A = animals, observation in vitro,
H = case report in humans
4. Herb/drug interactions reported in this table were obtained from a variety of literature sources. Many of the interactions listed are theoretical and the clinical relevance is unclear They are reported as they appeared in the publication with no attempt to verify the accuracy of the original information
