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by Dr. C.H. Weaver M.D. Updated 02/2022

Maybe you’re thinking that dietary supplements—vitamins and herbs—sound like a healthy addition to your nutrition and wellness plan. Some supplements may offer benefit, but there can be more to these unassuming capsules than you realize. Dietary supplements can actually cause serious side effects, including negative interactions with prescription medication. It’s therefore very important that you consult your doctor before trying any supplement.

According to Richard Tsong Lee, MD, medical director of the integrative medicine program at the University of Texas MD Anderson Cancer Center, “Herbs and supplements should be treated like prescription medication in that they have the potential to affect the body in both helpful and harmful ways.” Included in the potential risks of supplement use, according to Dr. Lee, are toxic effects at highly concentrated doses and interactions with prescription medications.

When it comes to safety, consider also that, unlike drugs, the US Food and Drug Administration (FDA) is not responsible for making sure a dietary supplement is safe before it goes on the market—even though supplements have the potential to cause complications similar to those of prescription medications. “Herbs and supplements are not regulated by the FDA, which means companies are not required to demonstrate efficacy, safety, or quality of the product made,” says Dr. Lee.

What are some potential negative outcomes associated with popular supplements? Dr. Lee cites two examples: beta-carotene (in supplement form) and Saint-John’s-wort. Beta-carotene, he says, has been associated with an increased risk of lung cancer, and Saint-John’s-wort (an herb thought to relieve mild depression) may interact adversely with the chemotherapy drugs Camptosar® (irinotecan) and Gleevec®(imatinib mesylate) as well as with the hormonal therapy tamoxifen (Nolvadex®).

Tell your doctor about current or planned supplement use if you are undergoing surgery—some supplements may cause side effects related to surgery. Certain supplements, for example, increase the risk of bleeding; these include garlic, ginkgo biloba, ginseng, and vitamin E. Others, such as kava and valerian, may need to be avoided because they can increase the sedative effects of anesthetics.

The two chief take-home messages about dietary supplement use are: First, never assume a product is safe, even if it’s labeled “natural.” Second, always talk with your doctor before trying any dietary supplement. With proper guidance and with safety as a priority, you may find that certain herbs and vitamins are a great addition to your wellness plan.


Used for: Depression

May interact with: Anti-cancer drugs (such as Camptosar® [irinotecan]), birth control medication, HIV/AIDS drugs, drugs used to prevent rejection of organ transplant, anticoagulants (drugs to prevent blood clotting), heart medication

Potential side effects: May increase sun sensitivity, anxiety, dry mouth, dizziness, fatigue, headache, gastrointestinal symptoms, sexual dysfunction


**Used for:**Inflammation and arthritis-related pain, liver function, digestion, menstrual irregularities, heartburn, stomach ulcers, gallstones, cancer treatment and prevention

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Potential side effects: Indigestion, may worsen gallbladder disease


Used for: Migraines, fevers, headaches, stomachaches, rheumatoid arthritis, psoriasis, allergies

Potential side effects: Canker sores, irritation and swelling of lips and tongue, nausea, bloating, digestive problems, allergic reactions; should not be taken by women who are pregnant due to risk of miscarriage and preterm delivery

Black Cohosh

Used for: Menopausal symptoms including hot flashes, night sweats, and vaginal dryness; menstrual irregularities and premenstrual syndrome; arthritis and muscle pain (also known as rheumatism)

Potential side effects: Liver complications, including abdominal pain, dark urine, or jaundice; reports of hepatitis and liver failure


Used for: Immune support, chronic hepatitis, common colds, and upper respiratory infections

May interact with: Medications to suppress immune system (such as those taken by cancer patients and patients undergoing organ transplant)

Potential side effects: Changes to blood pressure and blood sugar levels; some species can be toxic (not those usually found in dietary supplements, however)


Used for: Many health conditions; high cholesterol levels, menopausal symptoms, osteoporosis, high blood pressure, breast cancer, and prostate cancer

Potential side effects: Stomach irritation, including nausea, bloating, and constipation; allergic reactions; uncertain role in breast cancer and effects on estrogen levels—women at high risk of breast cancer are advised to discuss using soy with their healthcare providers