| |
| Use caution with | If you’re taking | Note |
| Calcium | Tetracycline | To avoid decreased absorption of tetracycline, simply take calcium two hours before or after the antibiotic. |
| Coenzyme Q10 | Warfarin | Not an absolute contraindication. If taking both, use caution and consider having a blood-clot test done to monitor any changes in prothrombin time. |
| Folic acid | The chemotherapy drug methotrexate and the epilepsy drugs phenobarbital, phenytoin, and primidone | Patients with acute lymphoblastic leukemia (ALL) should avoid folic acid in supplement form. |
| Garlic (Allium sativum) | Ticlopidine, warfarin | There is very little evidence to show that serious bleeding problems have developed from these combinations. |
| Iron | Carbidopa, ciprofloxacin, tetracycline, warfarin | An absorption issue; simply take iron two hours before or after the drug. |
| St. John’s wort (Hypericum perforatum) | Oral contraceptives; benzodiazepines; chemotherapy drugs; digoxin; antihistamines such as fexofenadine; antidepressants such as nefazodone, paroxetine, sertraline, trazodone, and tricyclic antidepressants; antiviral drugs such as atazanavir and indinavir; and warfarin | There are some documented cases of unwanted pregnancy that have occurred in women who added St. John’s wort to their birth control pills. |
| Vitamin C | Warfarin | Only a concern with very high doses of vitamin C; at least one study showed that taking up to 10 grams of vitamin C per day had no effect on warfarin’s anticoagulant effects. |
| Sources: Bob Rountree, MD; A–Z Guide to Drug-Herb-Vitamin Interactions by Alan R. Gaby, MD, et al. (Prima Publishing, 1999). |
