August 2020

New & Notable Drug-Supplement Interactions

New drug-supplement interactions are constantly being identified. Here are some new interactions that have recently been added to our database.

New animal research shows that taking berberine two hours before taking metformin might increase metformin levels in the body. This might increase the effects and side effects of metformin. Taking berberine and metformin at the same time doesn’t seem to have this effect.  While this interaction isn’t yet confirmed in humans, there’s evidence that taking berberine can help reduce blood sugar in people with diabetes, so this may be a clinically relevant interaction for many patients. Tell patients taking metformin to be cautious with berberine and berberine-containing natural ingredients, and to discuss any side effects with their provider.

While not new, there’s even more evidence in humans that drinking less than one cup of brewed green tea reduces how much nadolol the body absorbs – reducing the effectiveness of nadolol. A previous study found that nadolol absorption is reduced in people who have consumed green tea daily for the past 2 weeks. The newer study shows that green tea affects nadolol absorption even when it is consumed only once at the same time, or an hour before, taking nadolol. Tell patients who are taking nadolol to avoid drinking green tea or taking green tea products.

Finally, new animal data shows that taking cannabidiol (CBD) might reduce how quickly the body breaks down the anticonvulsant drug carbamazepine by inhibiting CYP3A4 enzymes. In theory, this might lead to increased effects and side effects from carbamazepine. Since this is a narrow therapeutic index drug with complex metabolism, make sure to discuss CBD use with patients taking carbamazepine.

We are constantly adding new interactions to our monographs as they are identified. Make sure to take advantage of our Interaction Checker – it allows you to quickly screen for interactions between natural medicines, including multi-ingredient supplements and conventional drugs. Using the interaction checker whenever a question or concern arises ensures that you will always be aware of interactions as they are identified.

The information in this brief report is intended for informational purposes only, and is meant to help users better understand health concerns. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions. Copyright © 2024 NatMed. Commercial distribution or reproduction prohibited. NatMed is the leading provider of high-quality, evidence-based, clinically-relevant information on natural medicine, dietary supplements, herbs, vitamins, minerals, functional foods, diets, complementary practices, CAM modalities, exercises and medical conditions. Monograph sections include interactions with herbs, drugs, foods and labs, contraindications, depletions, dosing, toxicology, adverse effects, pregnancy and lactation data, synonyms, safety and effectiveness.