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St. John's Wort (Mildac)
- MAOI (target mainly (at least) MAOAs) through some contained beta-carboline harmala alkaloids.
- Phloroglucinols (2–5%)
- Adhyperforin (0.2–1.9%)
- Hyperforin (2–4.5%)
- Naphthodianthrones (0.03-3%)
- Hypericin (0.003–0.3%)
- Pseudohypericin (0.2–0.23%)
- Flavonoids (2–12%)
- Amentoflavone (0.01–0.05%)
- Apigenin (0.1–0.5%)
- Catechin (2–4%)
- Epigallocatechin
- Hyperoside (0.5–2%)
- Kaempferol
- Luteolin
- Quercetin (2–4%)
- Rutin (0.3–1.6%)
- Phenolic acids (~0.1%)
- Caffeic acid (0.1%)
- Chlorogenic acid (<0.1%)
- It induces the cytochrome P450 system, particularly the CYP3A4 enzyme, and P-glycoprotein, which are critical for metabolizing and transporting various drugs. This induction can lead to increased metabolism of co-administered medications, potentially reducing their efficacy. For instance, a 2009 PMC article by Izzo highlights that St. John's wort induces CYP3A4, CYP2E1, and CYP2C19, with no effect on CYP1A2, CYP2D6, or CYP2C9, and notes that the primary site is intestinal CYP3A4, with effects returning to baseline after about a week (Herb–Drug Interactions with St John’s Wort (Hypericum perforatum): an Update on Clinical Observations).
- This induction is particularly relevant for drugs like digoxin, where a 33.3% decrease in trough concentration and 25% reduction in area under the curve (AUC) have been observed after 10 days of St. John's wort use. Such interactions are crucial for patients, as they can lead to reduced effectiveness of medications like cyclosporine, ethinylestradiol, and others, especially with low hyperforin extracts showing weaker effects.
Enzyme/Transporter Effect Examples of Affected Drugs Notes CYP3A4 Induced, increases metabolism Midazolam, cyclosporine Primary site is intestinal, half-life 46.2 h P-glycoprotein Induced, affects transport Digoxin, fexofenadine Effect seen after ≥10 days, no effect 1–3 days Hyperforin Role Potent inducer, determines interaction magnitude Alprazolam, tolbutamide Low hyperforin (<0.5%) shows weak effect - Specific interactions include:
- Cyclosporine, used in organ transplants, may have decreased effectiveness, risking rejection.
- Indinavir, an HIV protease inhibitor, may have reduced antiviral activity.
- Oral contraceptives may fail, increasing the risk of unintended pregnancy.
- Coumadin (warfarin) and digoxin levels may drop, affecting anticoagulation and heart function.
- Benzodiazepines, used for anxiety, may have diminished sedative effects.