Tygerberg, South Africa—Which commonly used herbal products have the potential to alter prescription drug effectiveness or create dangerous side effects?

The was the question addressed in a recent The British Journal of Clinical Pharmacology article. A study team led by South African researchers from the University of Stellenbosch analyzed published studies and reports and ended up cautioning against a number of the products. Included in the analysis were 49 case reports and two observational studies with 15 cases of adverse drug reactions.

Researchers searched electronic databases of PubMed, the Cochrane Library, Medline, and Scopus for randomized or nonrandomized clinical studies, case-control and case reports of herb-drug interactions (HDI). 

Results indicate that most of the patients affected had been diagnosed with cardiovascular diseases, 30.6%; cancer, 22.45%, and kidney transplants, 16.32% and were prescribed warfarin, alkylating agents, and cyclosporine, respectively. Researchers point out, for example, that patients using warfarin and/or statins for the treatment of cardiovascular complications reported significant interactions after taking herbal products including sage, flaxseed, St. John’s wort, cranberry, goji juice, green tea, and chamomille.

“HDI occurred in patients resulting in clinical ADRs with different severity,” study authors concluded. “Patients may poorly respond to therapeutic agents or develop toxicity due to severe HDI which in either scenario may increase the cost of treatment and /or lead to or prolong patient hospitalization. It is warranted to increase patient awareness of the potential interaction between herbs and prescribed medicines and their consequences to curb HDI as a potential health problem.”

On its website, the National Center for Complementary and Integrative Health emphasizes, “Although there is a widespread public perception that herbs and botanical products in dietary supplements are safe, research has demonstrated that these products carry the same dangers as other pharmacologically active compounds. Interactions may occur between prescription drugs, over-the-counter drugs, dietary supplements, and even small molecules in food—making it a daunting challenge to identify all interactions that are of clinical concern.”

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