In the last decade of the 20th century, the use of herbal remedies gained increasing popularity, especially in developed countries, as part of self-medication and disease prevention. However, while many believe that “natural” means “safe,” the use of herbal medicines carries certain risks. If information about a specific herbal product is not known or readily available, it is recommended, for safety reasons, to take herbal medicines at least two hours apart from conventional medications and to stop using herbal products at least seven days before any surgical procedure. Special caution is needed for patients taking drugs with a narrow therapeutic range, as combining them with herbal products may increase the risk of severe side effects, including reduced therapeutic efficacy.
In the European Union (EU), herbal preparations can be registered as herbal medicines, traditional herbal medicines, or dietary supplements. Herbal medicines are based on scientific evidence of safety and efficacy, while traditional herbal medicines rely on long-term medicinal use (at least 30 years). Unfortunately, a large number of herbal preparations are still registered as dietary supplements.
Although interactions with herbal preparations are generally less serious than those with synthetic drugs, many have not been adequately studied, and healthcare professionals are often uninformed about their patients’ use of herbal products. These interactions can include pharmacodynamic and pharmacokinetic changes that may reduce or enhance the therapeutic effects of medications. The mechanisms of these interactions are not fully understood but are often linked to the influence of herbal components on CYP450 enzymes and P-glycoproteins.
Pharmacodynamic and Pharmacokinetic Interactions
- Pharmacodynamic Interactions occur when a herbal preparation alters the therapeutic effect of a drug, either enhancing it (e.g., combining a herbal product with antiplatelet effects and warfarin) or reducing its efficacy (e.g., a herbal product blocking dopamine receptors and levodopa).
- Pharmacokinetic Interactions occur when a herbal preparation changes the absorption, distribution, metabolism, or excretion of a drug, affecting its activity. Notable interactions include antithrombotic agents (like warfarin), antidepressants, sedatives, cardiovascular drugs, immunosuppressants, and cytostatics. St. John’s Wort is particularly well-known for its interactions, such as with cyclosporine, a potentially serious combination.
St. John’s Wort (Hyperici herba)
St. John’s Wort is known for its antidepressant properties, with dry extracts showing effectiveness in treating mild to moderate depressive episodes. Traditionally, it has been used in folk medicine for alleviating psychological exhaustion and minor digestive issues, and topically for minor wounds. Its main active ingredients—hyperforin, hypericin, flavonoids, and naphthodianthrones—exhibit antidepressant effects by inhibiting neurotransmitter reuptake, including serotonin, norepinephrine, and dopamine.
Hyperforin can accelerate drug metabolism by inducing CYP450 enzymes (notably CYP3A4, CYP2C9, and CYP2C19) and increasing the expression of P-glycoprotein, responsible for drug transport across the intestinal epithelium. These interactions may lead to reduced therapeutic drug levels and efficacy, affecting immunosuppressants (e.g., cyclosporine, tacrolimus), antiviral drugs, cytostatics, anticoagulants, and oral contraceptives.
Ginkgo Leaf (Ginkgo folium)
Ginkgo leaf is used for treating circulatory and brain-related health issues. Its standardized extracts, containing flavonoid glycosides and terpene lactones, are effective in improving circulation, reducing dizziness, tinnitus, and treating peripheral vascular diseases like intermittent claudication. Ginkgo is also commonly used to enhance memory and concentration.
Although safe for long-term use, ginkgo may interact with antithrombotic and anticoagulant medications, potentially leading to spontaneous clotting or internal bleeding.
Senna Leaf/Fruit (Sennae folium/fructus) and Frangula Bark (Frangulae cortex)
These herbal medicines are used for short-term relief of occasional constipation. The active compounds, hydroxyanthracene derivatives, stimulate bowel motility and increase water and electrolyte absorption, aiding in bowel movement. Their use is limited to avoid dependence and electrolyte imbalances.
Bearberry Leaf (Uvae ursi folium)
Bearberry is used for treating mild urinary tract infections. Its active ingredient, arbutin, shows antibacterial effects at urinary pH levels of 8. However, its use should be limited to two weeks and avoided during pregnancy, breastfeeding, or in children under 12.
Black Cohosh (Cimicifugae rhizoma)
Black cohosh is commonly used for alleviating menopausal symptoms like hot flashes and sweating. While effective, its use is contraindicated in hormone-dependent tumors and requires medical consultation for combination with hormone replacement therapies.
Conclusion
The use of herbal medicines is becoming increasingly popular as part of self-medication and disease prevention. However, “natural” does not always mean “safe.” Herbal medicines can cause significant pharmacodynamic and pharmacokinetic interactions with conventional drugs, impacting therapy efficacy and increasing the risk of side effects.
Raising awareness among healthcare professionals and patients is essential. Doctors should routinely inquire about patients’ use of herbal products, while patients should consult their healthcare providers before using herbal medicines, especially when taking other medications.
Only through education, awareness, and coordination among healthcare providers, patients, and other stakeholders can the risks of harmful interactions be minimized and the safe use of herbal preparations in therapy ensured.
Prepared by:
MSc Pharm. Romana Galin
