Multivitamins and multiminerals can alter the effects of BP medications, diuretics, sulfa drugs, nonsteroidal anti-inflammator drugs (NSAIDs) and tretinoin (Avita, Renova, Retin-A) and isotretinoin (Anisteem, Claravis, Myorisan, Sotret). Tretinoin and isotretinoin, also known as retinoic acid, are forms of vitamin A normally used to treat acne. 


Fish oil, omega-3 fatty acids and dihydroxyacetone docosahexaenoic acid (DHA). These organic compounds, which are obtained primarily from fish and plants, have been shown to provide mild reductions in BP, reduce triglyceride levels and decrease clotting time, therefore providing a cardiovascular benefit. Reduction of inflammation and mild dilatation of the blood vessels have also been seen in studies involving fish oil and omega-3 fatty acids. However, there is some evidence that ingesting excessive amounts of fish oils can increase the risk of stroke.


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These compounds can worsen diabetes control and contribute to immune suppression, so their use in persons with autoimmune and immune-deficient conditions should be avoided. Fish oil, omega-3 fatty acids and DHA can alter the effectiveness of NSAIDs, celecoxib (Celebrex), clopidogrel (Plavix), warfarin (Coumadin, Jantoven), heparin, enoxaparin (Lovenox), orlistat (Alli, Xenical) and some BP medications.


Glucosamine and glucosamine chondroitin. While glucosamine and glucosamine chondroitin are primarily indicated for osteoarthritis and other joint problems, some effect has also been reported in persons with irritable bowel disorder.

Glucosamine is an amino acid compound derived primarily from proteins and shellfish. Therefore, persons with shellfish allergies must be diligent in checking labels to make sure they are not at risk for anaphylaxis from the ingredients, and emergency medicine providers need to question patients with no identifiable risk about supplements that might contain shellfish components. Glucosamine can alter the effectiveness of NSAIDs and diabetes agents, including insulin, and should be used cautiously in individuals taking potassium supplements and anticoagulants. 


Echinacea. Documented uses for echinacea can be traced to the Sioux Indians, who used it to treat snakebites, rabies and other systemic poisonings. Also known as purple cornflower and black sampson, echinacea is primarily used today for combating viral illness and as an immunity builder and is often combined in preparations with the herb goldenseal.

Echinacea should not be used by patients with immune disorders, such as multiple sclerosis, HIV disease or lupus, or by organ transplant recipients. Echinacea can also affect the actions of corticosteroids, antibiotics and diabetes medications. Neither echinacea nor goldenseal should ever be taken during pregnancy. 


Flax seed. Given its long list of health benefits, flax seed is a popular supplement and readily available for use, coming in a wide variety of preparations, including capsules, oils, teas, ground flour and whole seeds. It is often used in salad dressings and sprinkled on foods for easy consumption.

Flax seed has been recommended for use in asthma, colon health, cancer prevention, heart health and as an anti-inflammatory agent. It can slow the absorption of all medications and may alter the effects of blood thinners, diabetes medications, contraceptives, hormones and antihyperlipidemic agents. Immature seed pods can be poisonous, so consumers should buy flax seeds only from reputable vendors. 


Ginseng. Patients looking to counteract fatigue often try ginseng, which has been identified as a stimulant in both Asian and North American cultures. Available in a host of preparations, ginseng is used to treat multiple complaints, including sexual dysfunction, stomach disorders, fatigue and asthma. Ginseng does not seem to have any beneficial effect on persons who are already active or energetic, and it should not be taken in combination with products containing caffeine.

The drug/drug interaction potential of ginseng extends to diabetes medications, psychiatric drugs, opiate pain medications, blood thinners and thrombolytics, calcium channel blockers and NSAIDs. 


Vitamins. Vitamin-B complex is also sold as an energy booster, and while not having any scientific evidence to back the claim, vitamin B12 injections have a legendary anecdotal reputation of being a powerful fatigue fighter.One well-documented recommendation is that folic acid (vitamin B6) be used prior to and during pregnancy to lower the risk of neural tube defects, including spina bifida and anecephaly, by at least 50%.9 B-complex supplements are also recommended in treating skin disorders and peripheral neuropathies and for abnormalities in sensation of the tongue.

B-vitamin preparations can alter the effects of antidepressants, medications for gastroesophageal reflux, tetracycline, chemotherapy agents, metformin (Fortamet, Glucophage, Glumetza, Riomet), bile-acid sequestrants, levodopa and erythropoietin. 


Vitamin E has been touted for a variety of health concerns, including skin problems, menopausal symptoms, fibrocystic breast disease, diabetes, cardiovascular disease and cancer. Because vitamin E is fat-soluble, overdosing is possible, and the recommended dose of up to 10 to 30 mg daily should not be exceeded.

Even in recommended doses, vitamin E can contribute to thrombophlebitis, pulmonary embolism and gynecomastia. Iron supplementation can increase the need for vitamin E. Drugs that can be affected by concomitant use with vitamin E include antidepressants, beta blockers, anticoagulants, cholesterol medications, female replacement hormones, phenothiazines and others. 


Like vitamins B and E, vitamin C (ascorbic acid) also has a long list of beneficial uses as a natural medicine. Most commonly known for reportedly helping to prevent or cure the common cold, vitamin C also helps to enhance the absorption of iron and is considered to be beneficial in cancer treatment.10 Additionally, some protocols for treatment of Lyme disease use high doses of vitamin C in an IV solution. Vitamin C has also been used for the relief of menopausal symptoms, particularly hot flashes.

Ingestion of Vitamin C can interfere with or enhance the effects of NSAIDs, acetaminophen, aluminum-containing antacids, chemotherapy drugs, female hormone replacement, barbiturates, tetracycline, indinavir (Crixivan) and warfarin.


Calcium. Best-known for assisting in the prevention osteoporosis and enhancing bone health, calcium should be administered in commonly recommended doses of 1,200-2,000 mg/day along with vitamin D. Ingestion of calcium should be divided into 500-mg doses to provide the best absorption. Some studies link calcium to improved cardiovascular status, lower BP, weight loss and reduced incidence of colon cancer. Calcium deficiency can be associated with muscle cramping and weakness.